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Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Experimental Realization of an Achromatic Magnetic Mirror based on Metamaterials

Giampaolo Pisano, Carole Tucker, and Peter Ade

Doc ID: 260245 Received 29 Feb 2016; Accepted 23 May 2016; Posted 23 May 2016  View: PDF

Abstract: Our work relates to the use of metamaterials engineered to realize a meta-surface approaching the exotic properties of an ideal object not observed in nature, a ‘magnetic mirror’. Previous realizations were based on resonant structures which implied narrow bandwidths and large losses. The working principle of our device is ideally frequency-independent, it does not involve resonances and it does not rely on a specific technology. The performance of our prototype, working at millimetre wavelengths, has never been achieved before and it is superior to any other device reported in the literature, both in the microwave and optical regions. The device inherently has large bandwidth (144%), low losses (<1%) and is almost independent of incidence-angle and polarization-state and thus approaches the behaviour of an ideal magnetic mirror. Applications of magnetic mirrors range from low-profile antennas, absorbers to optoelectronic devices. Our device can be realised using different technologies to operate in other spectral regions.

Polarimetric parameters associated to special microstructured fibers

Marcelo Vaca-Pereira, Uladzimir (or Vladimir) Minkovich, Rafael Espinosa Luna, Yuri Barmenkov, and Sergio Calixto

Doc ID: 260995 Received 11 Mar 2016; Accepted 23 May 2016; Posted 23 May 2016  View: PDF

Abstract: The Mueller matrices associated to six home-made special index-guiding microstructured fibers are determined at a transmission wavelength of 1550 nm. Diattenuation, polarizance, retardance and polarization dependent loss (PDL), among other polarimetric parameters, are determined from the Mueller matrix associated to a 2 m length of each fiber studied here. Results show that the fiber fabrication parameters have a clear effect on the output degree of polarization, providing an inverse relationship between the degree of polarization output and the relative hole diameter, d/Λ value.

Controlling the propagation of optical vortex through two-dimensional ordered and disordered waveguide arrays using topological charge

Abbas Ghasempour Ardakani and Fatemeh Safarzadeh

Doc ID: 261166 Received 15 Mar 2016; Accepted 23 May 2016; Posted 23 May 2016  View: PDF

Abstract: In this paper, we study the propagation of a radially symmetric optical vortex whose amplitude is independent of topological charge in both ordered and disordered two-dimensional arrays of coupled waveguides. It is first demonstrated that the topological charge variation affects the beam spreading in the completely ordered arrays. For a low refractive index contrast between waveguides and their surroundings, the effective width at the output end of the optical lattice versus topological charge shows an oscillatory behavior. However, for a higher refractive index contrast, as topological charge increases from 0 to 10, the effective width reaches a maximum value and then falls. Then we investigate the effects of topological charge variation on the wave propagation through the waveguide array in the presence of different disorder strengths. Our results here confirm that the behavior of effective width versus the topological charge in the disordered array significantly depends on the average of the refractive index of the waveguides. Although the intensity of the input radially symmetric vortex beam is independent of the topological charge, for low disorder levels, the effective width and intensity distribution at the output end is strongly sensitive to the topological charge or the polar phase of the vortex beam. It is also demonstrated that for strongly disordered arrays, the effective width and output beam profile shows no considerable change with variation of the topological charge. These effects are due to the discrete diffraction phenomenon and its dependence on the helical wavefront of the optical vortex whose form is determined by the topological charge. Therefore, it is demonstrated here that angular phase affects the beam broadening in an array of coupled optical waveguides.

A subwavelength micropolarizer in a gold film for visible light

Sergey Stafeev, Victor Kotlyar, Maria Kotlyar, Anton Nalimov, and Liam O'Faolain

Doc ID: 261705 Received 22 Mar 2016; Accepted 23 May 2016; Posted 23 May 2016  View: PDF

Abstract: We have designed and fabricated a 100×100-µm four-sector binary subwavelength reflecting polarization micro-converter in a gold film. Using the FDTD-aided numerical simulation and experiments, the micropolarizer was shown to convert an incident linearly polarized Gaussian beam of wavelength 532 nm into an azimuthally polarized beam. Conditions for generating on-axis regions of non-zero intensity when using propagating optical vortices with different initial polarization were deduced. By putting a spiral phase plate into an azimuthally polarized beam the intensity pattern was shown to change from diffraction rings to a central peak.

In situ planktons and fishes detection based on optical gated sampling

Liu Xiaoquan, Xinwei Wang, zhou yan, and liu yuliang

Doc ID: 261916 Received 12 Apr 2016; Accepted 22 May 2016; Posted 23 May 2016  View: PDF

Abstract: For the in-situ detection technologies of planktons and fishes, optical cameras traditionally have a small and fixed sampling volume with a strong target sized dependent (typically <1mm), and imaging sonar has lower spatial resolution (typically > 2cm) with a problem of species identification. To solve the above problems, this paper proposes an in situ detection method of optical gated sampling for mm- to cm-scaled planktons and fishes detection. In this method, the sampling volume can be flexibly adjusted by matching the temporal parameters of gate pulses and illuminator laser pulses to satisfy target observation with different sizes. The gated sampling suppresses the backscattering of water and also filters environment background so that transparent planktons can be detected by high contrast. Furthermore, the sampling volume is determined by the convolution of gate pulses and laser pulses, and thus the target abundance is derived. Theory and simulation of abundance measurement are established. In experiments, transparent jellyfishes are recorded with a spatial resolution of better than 100 μm. In addition, the proof experiments of sampling volume adjustment and abundance measurement are demonstrated.

Coherent imaging with resonance domain diffractive lens in laser light

OMRI BARLEV and Michael Golub

Doc ID: 260445 Received 03 Mar 2016; Accepted 22 May 2016; Posted 23 May 2016  View: PDF

Abstract: We investigated coherent imaging with binary off-axis resonance domain diffractive lens under active in visible spectral range laser illumination. The relations between the dispersion of this lens, shape of its point spread function and spectral properties of the illumination were analyzed theoretically and experimentally. In particular, we measured the point spread function, imaging contrast and diffraction efficiency for typical laser wavelengths. Experimental results proved feasibility of imaging with low distortion and more than 83% diffraction efficiency in laser light.

An extended-field coverage hyperspectral camerabased on single-pixel

Senlin Jin, WangWei Hui, Bo Liu, Cuifeng Ying, Dongqi Liu, Qing Ye, Wen-Yuan Zhou, and Jian-Guo Tian

Doc ID: 259298 Received 24 Feb 2016; Accepted 20 May 2016; Posted 20 May 2016  View: PDF

Abstract: A spectral single-pixel imaging system facilitates effective image compression but the imaging region is limited byits single detector. This paper develops a hyperspectral camera that allows extended-field coverage to be collectedby one detector. The compressive data of the large field of view (LFOV) is achieved by our highly sensitive detectioncamera, which can be extended to near-infrared or infrared spectral monitoring. We acquire a hyperspectraldatacube of 256×256 spatial pixels and 3nm spectral resolution at a sampling rate of 25%. Finally, we apply ourcamera to monitoring fruit freshness nondestructively, by differentiating a banana’s ripeness over time.

Compact high-resolution Littrow conical diffraction spectrometer

Qinghua Yang

Doc ID: 263292 Received 14 Apr 2016; Accepted 20 May 2016; Posted 23 May 2016  View: PDF

Abstract: This paper presents a compact high-resolution Littrow conical diffraction spectrometer (LCDS) that includes an echelle grating for horizontally dispersing the incident light beam into several high diffraction orders, a prism for vertically separating the overlapping diffraction orders, and a shared focusing lens used for both the incident and dispersed beams. The unique design of the optics enables the LCDS to give high dispersion on the detector without requiring a large field of view and, therefore, to achieve the benefits of high spectral resolution and compactness. More particularly, the use of the Littrow conical diffraction coupled with the shared focusing lens makes the LCDS more compact. The formulas of the footprint of the dispersed spectra are derived, and the numerical simulation is given. The design calculations for application of the LCDS to an optical coherence tomography system are illustrated by an example.

Passive Q-switching of microchip lasers based on Ho:YAG ceramic

Xavier Mateos, Ruijun Lan, Pavel Loiko, Yicheng Wang, Jiang Li, Yubai Pan, Sun Young Choi, Mi Hye Kim, Fabian Rotermund, Anatol Yasukevich, Konstantin Yumashev, Uwe Griebner, and Valentin Petrov

Doc ID: 259558 Received 16 Feb 2016; Accepted 19 May 2016; Posted 20 May 2016  View: PDF

Abstract: A Ho:YAG ceramic microchip laser pumped by a Tm fiber laser at 1910 nm is passively Q-switched by single- andmulti-layer graphene, single-walled carbon nanotubes (SWCNTs) and Cr2+: ZnSe saturable absorbers (SAs).Employing SWCNTs, this laser generated an average power of 810 mW at 2090 nm with a slope efficiency of 68%and continuous-wave to Q-switching conversion efficiency of 70%. The shortest pulse duration was 85 ns at arepetition rate of 165 kHz and the pulse energy reached 4.9 μJ. The laser performance and pulse stability weresuperior compared to graphene-SAs even for different number of graphene layers (n = 1 to 4). A model fordescription of the Ho:YAG laser Q-switched by carbon nanostructures is presented. This modeling allowed us toestimate the saturation intensity for multi-layered graphene and SWCNT SAs to be 1.2±0.2 and 7±1 MW/cm2,respectively. When using Cr2+:ZnSe, the Ho:YAG microchip laser generated 11 ns / 25 μJ pulses at a repetition rateof 14.8 kHz.

Analysis and Improvement of Accuracy, Sensitivity and Resolution of Coherent Gradient Sensing Method

Xue Feng, Xuelin Dong, Zhiyin Duan, and Changxing Zhang

Doc ID: 255446 Received 22 Feb 2016; Accepted 19 May 2016; Posted 19 May 2016  View: PDF

Abstract: Coherent gradient sensing (CGS) method, one kind of shear interferometry sensitive to surface slope, has been applied to full-field curvature measuring for decades. However, its accuracy, sensitivity and resolution have not been studied clearly. In this paper, we analyze the accuracy, sensitivity and resolution for CGS method based on the derivation of its working principle. The results show that the sensitivity is related to the grating pitch and distance, and the accuracy and resolution are determined by the wavelength of the laser beam and the diameter of reflected beam. The sensitivity is proportional to the ratio of grating distance to its pitch while the accuracy will decline as this ratio increases. Besides, we demonstrate that using phase gratings as shearing element can improve the interferogram and enhance the accuracy, sensitivity and resolution. The curvature of a spherical reflector is measured by CGS with Ronchi gratings and phase gratings at different experimental parameters to illustrate this analysis. All of the results are quite helpful for CGS applications.

Modeling and analysis of distributed feedbackquantum dot passively mode-locked lasers

mohammad hasan yavari, Javad Rahimi, and Vahid Ahmadi

Doc ID: 261060 Received 15 Mar 2016; Accepted 19 May 2016; Posted 20 May 2016  View: PDF

Abstract: In this paper, we investigate numerically two proposed monolithic distributed feedback quantum dot passivelymode-locked lasers (DFB-QDMLL) with and without grating in the saturable absorber (SA) section in order toenhance two important performances of QDMLLs for ultrahigh-bit-rate and single mode applications. We find outthat depending on the length of the grating, optical pulses with duration of about 3~8ps at approximately 2nd and4th harmonics of cavity round-trip frequencies can be generated by the proposed structures. We also compare thetemporal and spectral behavior of these structures under specified bias conditions and SA length. It is shown thatDFB-QDMLL has the ability to generate optical pulses with more peak power than grating embedded saturabeabsorber (GESA-DFB-QDMLL) structure which generates shorter pulses with a narrower spectral bandwidth. Wealso show that DFB-QDMLL operates in a larger range of absorber voltage while the other structure is verysensitive to absorber voltage and it operates well for middle ranges of this parameter.

Mechanical analysis and force chain determination in granular materials using digital image correlation

Fanxiu Chen, Qi Zhuang, and Huixin Zhang

Doc ID: 259622 Received 04 Mar 2016; Accepted 18 May 2016; Posted 19 May 2016  View: PDF

Abstract: The mechanical behaviors of granular materials are governed by the grain properties and microstructure of the materials. We conducted experiments to study the force transmission in granular materials using plane strain tests. The large amount of nearly continuous displacement data provided by the advanced non-contact experimental technique of digital image correlation (DIC) has provided a means to quantify local displacements and strains at the particle level. The average strain of each particle could be calculated based on the DIC method, and the average stress could be obtained using Hooke’s law. The relationship between the stress and particle force could be obtained based on basic Newtonian mechanics and the balance of linear momentum at the particle level. This methodology is introduced and validated. In the testing procedure, the system is tested in real 2D particle cases, and the contact forces and force chain are obtained and analyzed. The system has great potential to analyze a real granular system and measure the contact forces and force chain.

Large radius of curvature measurement based onvirtual quadratic Newton rings phase-shiftingmoiré-fringes measurement method in a non-nullinterferometer

Zhongming Yang, Kailiang Wang, Jinlong Cheng, Zhishan Gao, and Qun Yuan

Doc ID: 260315 Received 01 Mar 2016; Accepted 18 May 2016; Posted 19 May 2016  View: PDF

Abstract: We propose a virtual quadratic Newton rings phase-shifting moiré-fringes measurement method in a non-nullinterferometer to measure the large radius of curvature for a spherical surface. In quadratic polar coordinatesystem, linear carrier testing Newton fringes interferogram and standard Newton fringes interferogram form themoiré patterns. The wavefront difference data between the testing and standard spherical surface can be retrievedfrom the moiré pattern after the low-pass filtering. Based on the wavefront difference data, a precise formula forradius of curvature calculation in the quadratic polar coordinate system is deduced. The retrace error in thenon-null interferometer can be calibrated by the multi-configuration model of the non-null interferometric systemin ZEMAX. The experimental results indicate that the measurement accuracy is better than 0.18% for a sphericalmirror which the radius of curvature is 41400mm.

Design of a polymer filled silicon nitride strip/slot asymmetric hybrid waveguide for realizing both flat dispersion and athermal operation

Bian Dandan, Shaowu Chen, xun lei, Guanshi Qin, and Zhanguo Chen

Doc ID: 260351 Received 01 Mar 2016; Accepted 18 May 2016; Posted 19 May 2016  View: PDF

Abstract: An asymmetric strip/slot hybrid silicon nitride waveguide is designed to simultaneously realize the athermal operation and flat dispersion. The slot filling and upper cladding materials are negative-TOC, low refractive index polyurethane acrylate (PUA), while the left and right cladding layers are positive-TOC, high refractive index silicon nitride. With suitable waveguide parameters selection, an optimum strip/slot hybrid silicon nitride waveguide exhibits an effective TOC of 1.31×10¯⁸/K at 1550nm, and flattened dispersion in the wavelength range from 1200nm to 1800nm with the maximum dispersion of 30.51ps/(nm•km), and the minimum of 10.89ps/(nm•km). The proposed hybrid waveguide has great potentials in building up the broadband athermal micro-resonator optical frequency combs.

New features of the nonlinearity specific to twophononscattering controlled by elastic waves withlinear losses: potentials for high resolution spectralanalysis

Adan Omar Arellanes Bernabe and Alexandre Shcherbakov

Doc ID: 260641 Received 07 Mar 2016; Accepted 18 May 2016; Posted 19 May 2016  View: PDF

Abstract: New physical details inherent in the non-collinear two-phonon light scattering controlled by ultra-high frequency elastic waves of finite amplitude are studied in wide-aperture crystals exhibiting moderate linear acoustic losses. Recently, it had been demonstrated that this regime of light scattering exhibits the specific acousto-optical nonlinearity with a set of unit-level maxima. Here, in addition to already developed by us analysis, we present an advanced analytical description of this phenomenon in the amplitude and frequency domains; and what is more, we orient it mainly at the second unit-level maximum. This nonlinearity together with the linear acoustic losses in an acousto-optical cell produces a new effect of nonlinear apodization. The light beam, leaving the cell, can suppress side lobes and grow the dynamic range within potential optical spectrum analysis. After that we characterize comprehensively an acousto-optical cell, made of calomel and working within the second maximum of two-phonon light scattering, as a dispersive optical component. Finally, the results of our proof-of-principal experiments with the calomel-made cell, operating in the chosen regime, are presented and discussed.

Transition of Lasing Modes in Polymeric Opal Photonic Crystal Resonating Cavity

Xuan-Ming Duan, Lan-Ting Shi, Meiling Zheng, Feng Jin, Xian-Zi Dong, Weiqiang Chen, and Zhensheng ZHAO

Doc ID: 262109 Received 29 Mar 2016; Accepted 18 May 2016; Posted 19 May 2016  View: PDF

Abstract: We demonstrate the transition of lasing modes in the resonating cavity constructed by polystyrene opal photoniccrystals and 7 wt % tert-butyl Rhodamine B doped polymer film. Both single mode and multiple mode lasingemission are observed from the resonating cavity. The lasing threshold is determined to be 0.81 μJ/pulse for singlemode lasing emission and 2.25 μJ/pulse for multiple mode lasing emission, respectively. The single mode lasingemission is attributed to photonic lasing resulting from the photonic bandgap effect of the opal photonic crystals,while the multiple mode lasing emission is assigned to random lasing due to the defects in the photonic crystals.The result would benefit for the development of low-threshold polymeric solid-state photonic crystal lasers.

Experimental capabilities of 0.4 petawatt, 1 shot/minScarlet laser facility for high energy density science

Patrick Poole, Christopher Willis, Rebecca Daskalova, Kevin George, Scott Feister, Sheng Jiang, Joseph Snyder, John Marketon, Douglass Schumacher, Kramer Akli, Linn Van Woerkom, Richard Freeman, and Enam Chowdhury

Doc ID: 262167 Received 29 Mar 2016; Accepted 18 May 2016; Posted 18 May 2016  View: PDF

Abstract: We report on the recently completed 400 TW upgrade tothe Scarlet laser at The Ohio State University. Scarletis a Ti:sapphire based ultra-short pulse system thatdelivers > 10 J in 30 f s pulses to a 2 μm FWHM focalspot, resulting in intensities exceeding 5 × 1021 W/cm2.The laser fires at a repetition rate of once per minuteand is equipped with a suite of on-demand and on-shotdiagnostics detailed here, allowing for rapid collectionof experimental statistics. As part of the upgrade, theentire laser system has been redesigned to facilitateconsistent, characterized high intensity data collectionat high repetition rates. The design and functionalityof the laser and target chambers is described along withinitial data from commissioning experimental shots.

Temperature measurements in metallized propellant combustion using hybrid fs/ps coherent anti-Stokes Raman scattering

Sean Kearney and Daniel Guildenbecher

Doc ID: 261059 Received 14 Mar 2016; Accepted 18 May 2016; Posted 18 May 2016  View: PDF

Abstract: We apply ultrafast pure-rotational coherent anti-Stokes Raman scattering (CARS) fortemperature and relative oxygen concentration measurements in the plume emanating from aburning, aluminized ammonium-perchlorate propellant strand. Combustion of these metal-basedpropellants is a particularly hostile environment for laser-based diagnostics, with intensebackground luminosity and scattering from hot metal particles as large as several hundredmicrons in diameter. CARS spectra that were previously obtained using nanosecond pulsedlasers in an aluminum-particle-seeded flame are examined and are determined to be severelyimpacted by nonresonant background, presumably as a result of the plasma formed byparticulate-enhanced laser-induced breakdown. Introduction of fs/ps laser pulses improvesCARS detection by providing time-gated elimination of strong nonresonant backgroundinterference. Single-laser-shot fs/ps CARS spectra were acquired from the burning propellantplume, with picosecond probe-pulse delays of 0 and 16 ps from the femtosecond pump andStokes pulses. At zero delay, nonresonant background overwhelms the Raman-resonantspectroscopic features. Time-delayed probing results in the acquisition of background-freespectra that were successfully fit for temperature and relative oxygen content. Temperatureprobability densities and temperature/oxygen correlations were constructed from ensembles of2several thousand single-laser-shot measurements with the CARS measurement volumepositioned within 3 mm or less of the burning propellant surface. The results show that ultrafastCARS is a potentially enabling technology for probing harsh, particle-laden flame environments.

Propagation of an optical vortex carried by a partially coherent Laguerre-Gaussian beam in turbulent ocean

Cheng Mingjian, Lixin Guo, Jiangting Li, Qingqing Huang, Qi Cheng, and Dan Zhang

Doc ID: 261580 Received 21 Mar 2016; Accepted 17 May 2016; Posted 18 May 2016  View: PDF

Abstract: The mathematical model of an optical vortex carried by a partially coherent Laguerre-Gaussian (LG) beam propagation in weak horizontal oceanic turbulent channels was developed, based on Rytov approximation theory. The effect of oceanic turbulence on the orbital angular momentum (OAM) mode probability density, signal OAM mode detection probability, and spiral spectrum of the partially coherent LG beams was analyzed. Our results indicated that optical turbulence in ocean environment produced much stronger effect on the optical vortex than that in atmosphere environment, the effective range of the signal OAM mode of LG beams with a smaller ratio of the mode crosstalk was limited only to several tens of meters in turbulent ocean. The existence of oceanic turbulence evidently induced OAM modes crosstalk and spiral spectrum spread. The spatial incoherence of the beam source would enhance the effect of turbulent aberrations on the signal OAM mode detection probability, and fully coherent vortex beams provided better performance than partially coherent ones. The effects of oceanic turbulence on the detection probability increased with the increase of radial and azimuthal mode orders, oceanic turbulent strength parameter and temperature-salinity balance parameter. Large wavelength of the vortex beam would help improve the performance of this quantum optical communication system. These results may be of interest for the potential application of vortex beams in the practical communication among the divers, submarines, and sensors in the ocean environment.

Wide-area and Omnidirectional Optical Detector Arrays Using Modular Optical Elements

Asaad Kaadan, Hazem Refai, and Peter LoPresti

Doc ID: 262125 Received 29 Mar 2016; Accepted 17 May 2016; Posted 19 May 2016  View: PDF

Abstract: This paper presents novel, modular optical detector arrays of various shapes and configurations. Recently developed Modular Optical Wireless Elements (MOWE) architecture serves as the basis for large and complex optical detector arrays that can be constructed as geometric shells and provide wide-area -even omnidirectional- field-of-view (FoV). Programmable optical modules synchronously sample the environment, and then route measurements to the user via a dedicated electrical backbone. The arrays are inexpensive, easy to construct, and can be made with homogeneous/inhomogeneous optical properties. Applications include remote sensing, motion detection, optical navigation, and medical imaging, among others. We present the MOWE detector array concept and analysis and design methodology, as well as a number of demonstrations.

Aero-optical effects of an optical seeker withsupersonic jet for hypersonic vehicles in near space

Guangming Guo, Bin Zhang, and Hong Liu

Doc ID: 262274 Received 01 Apr 2016; Accepted 16 May 2016; Posted 18 May 2016  View: PDF

Abstract: The aero-optical effects of an optical seeker with supersonic jet for hypersonic vehicles in near space wereinvestigated by three suits of cases, in which the altitude, angle of attack, and Mach number were varied in a largerange. The direct simulation Monte Carlo based on Boltzmann equation was used for flow computations and raytracing method was used to simulate beam transmission through the non-uniform flow field over optical window.Both imaging displacement and phase deviation were proposed as evaluation parameters, along with Strehl ratiowere used to quantitatively evaluate aero-optical effects. The results shown that aero-optical effects is quite weakwhen the altitude is greater than 30 km, the imaging displacement is related to the incident angle of a beam and itis minimal when the incident angle is approximately 15°. For reducing the aero-optical effects, the optimal locationof an aperture should be lay in the middle of optical window.

Amplified spontaneous emission from DCJTB encapsulated inmesostructured composite silica SBA-15

Dingke Zhang, Zhuojun Duan, Yu Wang, Peng Zhang, and Shijian Chen

Doc ID: 263572 Received 19 Apr 2016; Accepted 16 May 2016; Posted 18 May 2016  View: PDF

Abstract: Amplified spontaneous emission (ASE) characteristics of a red dye DCJTBencapsulated in a highly ordered mesoporous SBA-15 were studied. The mesoporouscomposite silica film loaded with organic dye has been successfully synthesized by asolgel reaction process and a simple postgrafting method at room temperature. Thespectrum narrowing phenomena has been observed when the composite film is pumped atλp= 532 nm by a Nd:YAG pulsed laser. There is a substantial reduction in the fullwidth at half-maximum of the emitting light, which is one of the signatures of thepresence of ASE. The ASE threshold and net gain, respectively, reached 0.03 mJ puls−1and 34.7 cm-1 for the DCJTB encapsulated in mesoporous SBA-15 film. The optimizedASE properties owes much to the effects of the better spatial confinement of themolecules in the ordered mesoporous structure of the host SBA-15.

Characterization of drying paint coatings by dynamic speckle and holographic interferometry measurements

Nicolás Budini, Cecilia Mulone, Nicolás Balducci, Fabio Vincitorio, Ana López, and Alberto Ramil

Doc ID: 261501 Received 21 Mar 2016; Accepted 16 May 2016; Posted 18 May 2016  View: PDF

Abstract: In this work we implemented dynamic speckle and holographic interferometry techniques to characterize the drying process of solvent-based paint coatings. We propose a simple way to estimate drying time by measuring speckle activity and incrementally fitting experimental data through standard regression algorithms. This allowed us predicting drying time after about 20-30 min of paint application, which is fast regarding usual times required to reach the so-called tack-free state ($\approx$ 2 h). In turn, we used holographic interferometry to map small thickness variations of the coating surface during drying. We also demonstrate that results obtained from both techniques correlate to each other, which allows improving the accuracy of the drying time estimation.

Influence of gas humidity on the reflection coefficient of multilayer dielectric mirrors

Alexei Lugovskoi, Viktor Serdyukov, and Leonid Sinitsa

Doc ID: 259291 Received 09 Mar 2016; Accepted 16 May 2016; Posted 18 May 2016  View: PDF

Abstract: The influence of water vapor on the reflection coefficient of multilayer mirrors was studied using a gas cell with multiple reflection from the mirrors. A strong change in the reflection coefficient of the mirrors (up to 0.9%) was found when water vapor under pressure of mbar was injected into the cell, which was interpreted as a change in the refraction index of the layers of multilayer coatings when water vapor penetrated the porous coating structure.

Thin film multilayer filters for solar EUV telescopes

Nikolay Tsybin, Nikolay Chkhalo, Mikhail Drozdov, Evgeniy Kluenkov, Sergey Kuzin, Alexey Lopatin, Valery Luchin, Nikolay Salashchenko, and Sergey Zuev

Doc ID: 262111 Received 29 Mar 2016; Accepted 16 May 2016; Posted 16 May 2016  View: PDF

Abstract: Al with a passband in the wavelength range 17–60 nm and Zr with a passband in the wavelength range 6.5–17 nm thin films on a support grid or support membrane are frequently used as UV, visible and near-IR blocking filters in solar observatories. Possessing acceptable optical performance, filters have such shortcomings as low mechanical strength and low resistance to oxidation. These shortcomings hinder meeting the requirements of filters of future telescopes. We propose multilayer thin film filters on the base of Al, Zr and other materials with improved characteristics. It was demonstrated that stretched multilayer films on a support grid with a mesh size up to 5 mm can withstand vibration loads occurring during spacecraft launch. A large mesh size is preferable for filters of high resolution solar telescopes, since it allows image distortion caused by light diffraction on the support grid to be avoided. We have investigated the thermal stability of Al/Si and Zr/Si multilayers assuming their possible application as filters in the “Intergelioprobe” project, in which the observation of coronal plasma will take place close to the Sun. Zr/Si films show high thermal stability and may be used as blocking filters in the wavelength range 12.5–17 nm. Al/Si films show lower thermal stability: significant decreasing of the film’s transmission in the EUV spectral range and increasing in the visible spectrum have been observed. We suppose that the low thermal stability of Al/Si films restricts their application in the “Intergelioprobe” project; thus there is a lack of filters for the wavelength range λ > 17 nm. Be/Si and Cr/Si filters have been proposed for the wavelength range near 30.4 nm. Although these filters have lower transparency than Al/Si, they are superior in thermal stability. Multilayer Sc/Al filters with relatively high transmission at a wavelength of 58.4 nm (HeI line) and simultaneously sufficient rejection in the wavelength range near 30.4 nm (HeII line) have been fabricated. They are planned to be used in the project KORTES, whose telescopes will have EUV channel 58.4 nm.

Boundary Condition Thermometry using a Thermographic-Phosphor-Coated Thin Filament

Nathan Kempema and Marshall Long

Doc ID: 259211 Received 09 Feb 2016; Accepted 16 May 2016; Posted 16 May 2016  View: PDF

Abstract: Thermographic phosphors (TPs) exhibit a temperature sensitive emission spectrum when excited with ultraviolet radiation. In this study, 14 μm diameter SiC fibers are coated with ZnO or Dy:YAG using a ceramic binder to a total diameter of 70 ± 9 μm. ZnO and Dy:YAG fibers were used to measure fiber temperatures in the range of 294-450 K and 450-1245 K, respectively. The coated fiber provides higher signal levels compared to TP particle seeding and is no more invasive than the commonly used thermocouple. A calibration is performed to relate fiber temperature to the ratio of luminescent signal collected within two different bands of the fiber emission spectrum. Temperature was measured along the inlet of a series of nitrogen diluted ethylene diffusion flames stabilized on the Yale coflow burner to determine suitable thermal boundary conditions for computational modeling. The boundary condition temperatures were derived from a spline fitting of data acquired from the two fiber types in order to obtain fiber temperature sensitivity from 294-1245 K. The peak near-burner temperature is found to be higher than ambient conditions and to increase and shift its location radially outward with increased fuel percentage.

Phase gradient algorithm method for 3-D holographic ladar imaging

Jason Stafford, David Rabb, and Bradley Duncan

Doc ID: 259892 Received 24 Feb 2016; Accepted 15 May 2016; Posted 16 May 2016  View: PDF

Abstract: 3-D holographic ladar uses digital holography with frequency diversity to add the ability to resolve targets in range. A key challenge is that since individual frequency samples are not recorded simultaneously, differential phase aberrations may exist between them making it difficult to achieve range compression. We describe steps specific to this modality so that phase gradient algorithms (PGA) can be applied to 3-D holographic ladar data for phase corrections across multiple temporal frequency samples. Substantial improvement of range compression is demonstrated with a laboratory experiment where our modified PGA technique is applied. Additionally, the PGA estimator is demonstrated to be efficient for this application and the maximum entropy saturation behavior of the estimator is analytically described.

Convex optimization based windowed Fourier filtering with multiple windows for wrapped phase denoising

Kohei Yatabe and Yasuhiro Oikawa

Doc ID: 260304 Received 01 Mar 2016; Accepted 15 May 2016; Posted 16 May 2016  View: PDF

Abstract: The windowed Fourier filtering (WFF), defined as a thresholding operation in the windowed Fourier transform (WFT) domain, is a successful method for denoising a phase map and analyzing a fringe pattern. However, it has some shortcomings such as extremely high redundancy, which results in high computational cost, and difficulty on selecting an appropriate window size.In this paper, an extension of WFF for denoising a wrapped phase map is proposed. It is formulated as a convex optimization problem using Gabor frames instead of WFT. Two Gabor frames with differently sized windows are used simultaneously so that the above-mentioned issues are resolved. In addition, a differential operator is combined with a Gabor frame in order to preserve discontinuity of the underlying phase map better. Some numerical experiments demonstrate that the proposed method is able to reconstruct a wrapped phase map even for severely contaminated situation.

Q-switched Fiber Laser Based on Acoustooptic Modulator with the Injection Seeding Technique

Qinghe Mao, WENCAI LI, HAOWEI LIU, JI ZHANG, HU LONG, and Sujuan Feng

Doc ID: 260794 Received 08 Mar 2016; Accepted 15 May 2016; Posted 16 May 2016  View: PDF

Abstract: The operation mechanism and the pulse property of actively Q-switched erbium-doped fiber laser based on AOM switch with the injection seeding technique are investigated. Our results show that the Q-switched pulses can be locked to oscillate near a fixed frequency higher than that of the seed laser, though the frequency-shift effect of the AOM impedes stable cavity-mode oscillations. The operation mechanism of such Q-switch fiber lasers can be explained by the mutual locking-in among the shifted frequency components originated from the injected coherence seed with the help of the gain dynamics of the Q-switch cavity. Moreover, narrow-linewidth Q-switched pulses with different repetition rates can be obtained with different cavity lengths for incredibly stable output pulses without any use of cavity-stabilized techniques.

Region-confined restoration method for motion-blurred star image of the star sensor under dynamic conditions

Liheng Ma, Franco Zazzera, Guangwen Jiang, Xingshu Wang, Zongsheng Huang, and Shiqiao Qin

Doc ID: 260768 Received 08 Mar 2016; Accepted 15 May 2016; Posted 18 May 2016  View: PDF

Abstract: Under dynamic conditions, the centroiding accuracy of the motion-blurred star image decreases and the number of identified stars reduces, which leads to the degradation of the attitude accuracy of the star sensor. To improve the attitude accuracy, a region-confined restoration method, which concentrates on the noise removal and SNR improvement of the motion-blurred star images, is proposed for the star sensor under dynamic conditions. A multi-seed regions growing technique with the kinematical recursive model for star image motion is given to find the star image regions and to remove the noises. Subsequently, a restoration strategy is employed in the extracted regions, taking the time consumption and SNR improvement into consideration simultaneously. Simulation results indicate that the region-confined restoration method is effective in removing noises and improving the centroiding accuracy. The identification rate and the average number of the identified stars in the experiments verify the advantages of the region-confined restoration method.

Loop gain stabilizing with an all-digital automaticgain-control method for high precision fiber opticgyroscope

Yue Zheng, Zhang Chunxi, Lijing Li, Lailiang Song, and Wen Chen

Doc ID: 261095 Received 15 Mar 2016; Accepted 13 May 2016; Posted 16 May 2016  View: PDF

Abstract: For a fiber optic gyroscope (FOG) using electronic dithers to suppress the dead zone, without a fixed loop gain, thedeterministic compensation for the dither signals in the control loop of the FOG cannot remain accurate, resultingin the dither residuals in the FOG rotation rate output and the navigation errors in the inertial navigation system.An all-digital automatic-gain-control method for stabilizing the loop gain of the FOG is proposed. By using aperturbation square wave to measure the loop gain of the FOG and adding an automatic gain control loop in theconventional control loop of the FOG, we successfully obtain the actual loop gain and make the loop gain convergeto the reference value. The experimental results show that in the case of 20% variation in the loop gain, the ditherresiduals are successfully eliminated and the standard deviation of the FOG sampling outputs is decreased from2.00 deg/h to 0.62 deg/h (sampling period 2.5 ms, 10 points smoothing). With this method, the loop gain of the FOGcan be stabilized over the operation temperature range and in the long time application, which provides a solidfoundation for the engineering applications of the high precision FOG.

Performance analysis of fiber-based free-space optical communicationswith coherent detection spatial diversity

Kangning Li, Ma Jing, Liying Tan, Siyuan Yu, and Chao Zhai

Doc ID: 261884 Received 24 Mar 2016; Accepted 13 May 2016; Posted 16 May 2016  View: PDF

Abstract: The performances of fiber-based free-space optical (FSO) communications over Gamma-Gamma distributed turbulence are studied for multiple apertures receiver system. Equal gain combining (EGC) technique is considered as a practical scheme to mitigate the atmospheric turbulence. Bit-error rate (BER) performances for binary phase-shift keying (BPSK) modulated coherent detection fiber-based free space optical communications are derived and analyzed for EGC diversity receptions through an approximation method. To show the net diversity gain of multiple apertures receiver system, BER performances of EGC are compared with a single monolithic aperture receiver system with the same total aperture area (same average total incident optical power on the aperture surface) for fiber-based free space optical communications. The numerical results are verified by Monte-Carlo (MC) simulations. System performances are also compared for EGC diversity coherent FSO communications with or without considering fiber-coupling efficiencies.

Fused fiber micro-knots

Moti Fridman, shir shahal, avi Klein, and Gilad Masri

Doc ID: 262829 Received 08 Apr 2016; Accepted 13 May 2016; Posted 16 May 2016  View: PDF

Abstract: We present fusing of fiber micro-knot by a $CO_2$ laser beams. We demonstrate tuning of the coupling strength and tuning of the spectral resonance of the micro-knot by the fusing process. The experimental results reveal that fusing the fiber micro-knots increases the coupling efficiency, and improves the robustness and the stability of the micro-knots.

Phase retrieval based attacks on Linear Canonical Transform based DRPE systems

John Sheridan, Changliang Guo, and Inbarasan Muniraj

Doc ID: 260637 Received 10 Mar 2016; Accepted 13 May 2016; Posted 16 May 2016  View: PDF

Abstract: Hybrid Input Output algorithm(HIOA), Error Reduction algorithm(ERA) and combinations of both phase retrievalalgorithms (ER/HIOA) are applied to perform Ciphtertext Only Attacks (COA) on Linear Canonical Transform (LCT)based Amplitude Encoding (AE) Double Phase Random Phase Encryption (DRPE) systems. Special cases of LCTbased DRPE systems, i.e. Fourier (FT), Fractional Fourier (FRT) and Fresnel transform (FST) based DRPE, can alsobe successfully attacked using the method proposed. Numerical simulations are performed to demonstrate theefficacy of the proposed attacking method.

Ptychography for optical metrology with limited translation knowledge

Dustin Moore and James Fienup

Doc ID: 260663 Received 07 Mar 2016; Accepted 13 May 2016; Posted 16 May 2016  View: PDF

Abstract: We introduce unknown-transverse translation diversity phase retrieval (UTTDPR): a ptychographic algorithm for optical metrology when a subaperture is translating though a plane conjugate to the exit pupil in a very poorly known fashion. The algorithm estimates the direction of translation and the distance traveled by the subaperture from one point spread function (PSF) to the next.

A self-homodyne free space optical communication system based on orthogonal polarized BPSK

Guangyu Cai, Jianfeng Sun, Guangyuan Li, Guo Zhang, Mengmeng Xu, Bo Zhang, Chaolei Yue, and Liren Liu

Doc ID: 261381 Received 17 Mar 2016; Accepted 13 May 2016; Posted 13 May 2016  View: PDF

Abstract: A self-homodyne laser communication system based on orthogonal polarized BPSK was illustrated and demonstrated. The working principles of this method and the transceiver’s structure were elaborated aided with equations. Moreover, the SNR, sensitivity and BER in the amplifier noise limited case were analyzed. The reported experiment validates this method’s feasibility and proves its sensitivity advantages as a self-homodyne communication system.

Two Dimensional Analytical Modeling of a Linear Variable Filter for Spectral Order Sorting

Cheng-Hao Ko, Yueh-Hsun Wu, JIH-RUN TSAI, BANG-JI WANG, and Symphony Chakraborty

Doc ID: 261235 Received 17 Mar 2016; Accepted 12 May 2016; Posted 12 May 2016  View: PDF

Abstract: A two dimensional thin film thickness model based on the geometry of the commercial coater which can calculate more effectively the profiles of LVFs has been developed by isolating the substrate plane as an independent coordinate (local coordinate) whereas the rotation and translation matrix is used to establish the coordinate transformation and combine the characteristic vector with the step function to build a borderline which can conclude that the local mask will block the deposition or not. The height ofthe local mask has been increased up to 40 mm in the proposed model and two dimensional simulations are developed to obtain a thin film profile deposition on the substrate inside the evaporation chamber to achieve the specific request of producing LVF zone width in a economical way than the previously reported (Ko et al. (2015), Opt. Express).

CHARACTERIZATION OF PROSPECTIVE EXPLOSIVE MATERIALS USING TERAHERTZ TIME DOMAIN SPECTROSCOPY

Norbert Palka, Mateusz Szala, and Elzbieta Czerwinska

Doc ID: 259550 Received 17 Feb 2016; Accepted 11 May 2016; Posted 16 May 2016  View: PDF

Abstract: We investigated six prospective explosive materials in the terahertz range using time domain spectroscopy. A family of energetic azotetrazolate salts and two caged nitramines were studied. A number of distinct spectral features were observed in the 0.8–3.2 THz frequency range. In transmission configuration in ambient temperature we determined both the absorption coefficient and the refractive index of the materials, which were compressed as pellets. Since the visibility of some absorption peaks was not clear, additionally we performed characterization of these materials in a temperature range from -175 to 0 OC, which resulted in highlighting peaks with low amplitude. Since the considered explosives are insensitive to compression, we also measured them using an attenuated total reflection (ATR) technique, in which sample preparation is easier than with pressed pellets. The absorption peaks measured by ATR agree well with those determined in transmission. This suggests that ATR can also be used for identification of these classes of materials.

Supercontinuum based absorption spectrometer for cycle-resolved multi-parameter measurements in a rapid compression machine

Thomas Werblinski, Stefan Kleindienst, Rainer Engelbrecht, Lars Zigan, and Stefan Will

Doc ID: 257372 Received 14 Jan 2016; Accepted 11 May 2016; Posted 13 May 2016  View: PDF

Abstract: In this work we present a broadband supercontinuum based absorption spectrometer capable of cycle-resolved multi-parameter measurements at C engine conditions. Three parameters, temperature, pressure and water mole fraction can be extracted from broadband near-infrared H2O absorption spectra, spanning the wavelength-range from 1340 to 1405.5 nm, which exhibits a large number of specific H2O transitions. The spectrometer is based on spatial domain detection and features a near-infrared line scan camera as detector. Measurements were performed during a compression cycle of the RCM comprising a pressure and temperature range from 2.5 to 65 bar and 300 to 900 K, respectively. With the new spectrometer we are able to perform measurements within a complete compression and expansion stroke at measurement rates up to 50 kHz. A detailed overview is provided about the best match algorithm between theory and experiments, including parameters from two different spectral databases, namely the Barber-Tennyson database (BT2) and HITRAN2012. The results indicate that spectral broadening effects are notproperly described by theory, especially at pressure levels exceeding 20 bar, which results in a clear underestimation of the optically derived pressure data. Nevertheless, temperature can be determined accurately by performing a three-parameter fit based on H2O mole fraction, temperature and pressure. In contrast, making use of pressure transducer data as look-up values and varying only temperature and H2O mole fraction to find the best match leads to a clear overestimation of temperature at elevated pressures.

Refractive index gratings in electro-optic polymer thin films

Dijana Bogunovic, Sebastiampillai Raymond, Stefaan Janssens, David Clarke, Owen Bodley, Simon Ashforth, Miriam Simpson, and James Quilty

Doc ID: 261130 Received 15 Mar 2016; Accepted 10 May 2016; Posted 10 May 2016  View: PDF

Abstract: Refractive index gratings have been inscribed in polymer thin films by permanently photobleaching the organic chromophore PYR-3 dopant. The grating inscription process was investigated in detail for the purpose of improving the diffraction efficiency η of the PYR-3 doped polymer gratings.Three processes were identified that contributed to the η of the first diffracted order: a periodic change in the refractive index due to photobleaching of the PYR-3, formation of the surface relief grating as a consequence of free volume change during bleaching and the introduction of periodic, strain induced change in the refractive index.

Infrared shutter using cholesteric liquid crystal

Gyu Jin Choi, Jin Seog Gwag, Seung Hee Lee, and Hye Min Jung

Doc ID: 261935 Received 25 Mar 2016; Accepted 10 May 2016; Posted 10 May 2016  View: PDF

Abstract: In this paper we propose an infrared light shutter device using cholesteric liquid crystals (LCs). The pitch of the device corresponds to the wavelengths of the infrared region with a strong thermal effect. This device is intended for use as a smart window is to maintain an optimal indoor temperature by controlling the infrared radiation coming from the sun. The proposed cholesteric device switches between the planar state and the isotropic state by controlling the temperature using an electrically heated transparent electrode made of indium tin oxide (ITO). A window with a planar state that reflects infrared radiation would be used mainly in summer, while the isotropic state that transmits infrared would be applied in winter. The proposed device produced a variety of grey levels of transmittance based on temperature, and thus it can provide a proper temperature for each user. The easy fabrication process gives it appeal as a functional device in the smart window market, and it compares favorably with previous light shutter devices. The infrared shutter is expected to be useful for next-generation window applications.

A laser confocal radius measurement method for unpolished spheres

Weiqian Zhao, Xu Wang, Lirong Qiu, and Shuai Yang

Doc ID: 263575 Received 19 Apr 2016; Accepted 10 May 2016; Posted 10 May 2016  View: PDF

Abstract: A laser confocal radius measurement method for unpolished spheres (CRMUS) is proposed for measuring the radius of an unpolished sphere during the optical sphere processing. CRMUS uses the laser confocal focusing technique to accurately identify the cat’s eye and confocal positions of the unpolished sphere, and then uses the distance between the cat’s eye and confocal positions measured by a distance measurement interferometer to derive the radius. The partially coherent optical theoretical model of the CRMUS derived indicates that the CRMUS is able to measure the radius of the unpolished sphere with the roughness less than 0.15μm. Using an unpolished sphere made of Schott BK7 as the test sphere, experimental results indicate that the CRMUS has a relative expanded uncertainty less than 20ppm. The CRMUS could greatly increase the processing efficiency.

Simple parametric model for intensity calibration of Cassini CIRS data

John Brasunas, Nicolas Gorius, and Andrei Mamoutkine

Doc ID: 260157 Received 29 Feb 2016; Accepted 10 May 2016; Posted 11 May 2016  View: PDF

Abstract: Accurate intensity calibration of a linear Fourier transform spectrometer typically requires the unknown target and the two calibration targets to be acquired under identical conditions. We present a simple model, suitable for vector calibration, that enables accurate calibration via adjustments of measured spectral amplitudes and phases when these three targets are recorded at different detector or optics temperatures.

Towards a mid-IR femtosecond laser system with suspended-core tungstate-tellurite glass fibers

Elena Anashkina, Alexey Andrianov, Vitaly Dorofeev, and Arkady Kim

Doc ID: 261300 Received 25 Mar 2016; Accepted 10 May 2016; Posted 11 May 2016  View: PDF

Abstract: A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 μm range is discussed. This design incorporates conventional femtosecond near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 μm and of DW generation beyond 5 μm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

The Effect of Changing Speckles in Digital Holographyon Measurements of Static and VibratoryDisplacements

Karl Stetson

Doc ID: 261348 Received 22 Mar 2016; Accepted 10 May 2016; Posted 11 May 2016  View: PDF

Abstract: This paper presents a study of speckle effects observed in measurements of static and vibratory displacements bydigital holography. Such effects are shown to arise from changes in speckle fields that often occur betweenholographic recordings. These may be between recording holograms before and after static deformations, orchanges in image speckles for sets of holograms recorded for vibration measurement. If the speckle field itself doesnot change between such recordings, the effects appear to be limited mainly to round-off errors.

Correlation coefficient measurement of the mode-locked laser tones using four-wave mixing

Aravind Anthur, Vivek Panapakkam, Vidak Vujicic, Kamel Merghem, Abderrahim Ramdane, Liam Barry, and Francois LeLarge

Doc ID: 259881 Received 24 Feb 2016; Accepted 10 May 2016; Posted 10 May 2016  View: PDF

Abstract: We use four-wave mixing to measure the correlation coefficient of comb tones in a quantum-dash mode-locked laser under passive and active locked regimes. We study the uncertainty in the measurement of the correlation coefficient of the proposed method.

Calibration free wavelength modulation spectroscopy:Symmetry approach and residual amplitudemodulation normalization

Amiya Behera and Anbo Wang

Doc ID: 260475 Received 07 Mar 2016; Accepted 09 May 2016; Posted 10 May 2016  View: PDF

Abstract: A simple and novel strategy is reported for practical implementation of Wavelength Modulation Spectroscopy(WMS) with tunable diode laser. It eliminates the need for pre-characterization of laser intensity parameters ormaking any design changes to the conventional WMS system. Consequently, sensitivity and signal strength remainsame as that obtained from traditional WMS setup at low modulation amplitude. Like previously proposedcalibration-free approaches, this new method also yields absolute absorption line shape function. ResidualAmplitude Modulation (RAM) contributions present in the first and second harmonic signals of WMS are recoveredby exploiting their even or odd symmetric nature. These isolated RAM signals are then used to estimate theabsolute line shape function and thus removing the impact of optical intensity fluctuations on measurement.Uncertainties and noises associated with the estimated absolute line shape function, and the applicability of thisnew method for detecting several gases in the near infrared region are also discussed. Measurements of the1650.96 nm absorption line for 1% and 8% Methane concentration in 60 to 100 kPa pressure range are used tovalidate the efficacy of this new RAM recovery technique and demonstrate a calibration free system. As thisapproach has minimal dependency on diode laser operating conditions, it is more robust and suitable fordeployment in harsh industrial environments.

Effects of spectral parameters on the light propertiesof red-green-blue white light-emitting diode

Mingsheng Xu, Haoxiang Zhang, quanbin zhou, and Hong Wang

Doc ID: 256646 Received 11 Jan 2016; Accepted 09 May 2016; Posted 09 May 2016  View: PDF

Abstract: Red-green-blue white light-emitting diodes (RGB-WLEDs) have a great potential as commercial solid-state lighting devices as well asvisible light communication because of their high color rendering index (CRI) and high response frequency. The quality of light of a RGB-WLEDstrongly depends on its spectral parameters. In this study, we fabricated RGB-WLEDs with red, blue, green LEDs and measured the spectralpower distribution (SPD). The experimental SPD consistent with the calculated spectrum. We also measured the SPDs of LEDs with differentpeak wavelengths and extracted the spectral parameters, which were then used for modeling. We studied the effect of the wavelength and thefull width at half maximum (FWHM) on both the color rendering index and the luminous efficiency (LE) of the RGB-WLED using simulations.We find that the LE improves as the wavelength of the blue LED increases and the wavelength of red LED decreases. When the wavelength ofthe green LED increases, the LE increases first, but later it decreases. The CRI of the RGB-WLED increases with the wavelengths of the red, blueand green LEDs first but then decreases. The optimal wavelengths and FWHMs for maximum color-rendering and LE of the blue, green andred LEDs are 466nm, 536 nm, 606 nm and 26.0 nm, 34.0 nm and 19.5 nm.

Numerical analysis of double chirp effect in taperedand linearly chirped fiber Bragg gratings

Tomasz Osuch, Konrad Markowski, and Kazimierz Jędrzejewski

Doc ID: 259820 Received 22 Feb 2016; Accepted 09 May 2016; Posted 09 May 2016  View: PDF

Abstract: In this paper theoretical analysis of recently developed tapered chirped fiber Bragg gratings (TCFBG) written in codirectionaland counter-directional configurations is presented. In particular, the effects of synthesis of chirpsresulting from both fused taper profile, and linearly chirped fringe pattern of the induced refractive index changeswithin the fiber core, are extensively examined. For this purpose, a numerical model based on the transfer matrixmethod (TMM) and coupled mode theory (CMT) was developed for such a grating. The impact of TCFBG parameterssuch as grating length and steepness of the taper transition, as well as the effect of fringe pattern chirp rate onspectral properties of resulting gratings, are presented. Results show that by using the appropriate design process,TCFBGs with reduced or enhanced resulting chirp, and thus with widely tailored spectral responses, can be easilyachieved. In turn, it reveals great potential application of such structures. Presented numerical approach providesexcellent tool for TCFBG design.

Birefringent dual-frequency laser Doppler velocimeterusing a low-frequency lock-in amplifier technique forhigh resolution measurements

Hongbin Zhu, Jun Chen, Dongmei Guo, Wei Xia, Hui Hao, and Ming Wang

Doc ID: 260296 Received 01 Mar 2016; Accepted 09 May 2016; Posted 09 May 2016  View: PDF

Abstract: A birefringent dual-frequency laser with a half-intracavity has been used to develop a laser Doppler velocimeter(LDV). The developed LDV utilizes a new signal-processing method based on the lock-in amplifier to achieve highresolutionvelocity measurements and the discrimination of positive and negative velocities. Theoretical analysisand simulation results are presented. The velocity measurement experiments by using a high-precision linearstage are performed to verify the performance of the LDV. Compared with the previous dual-frequency LDV, theaverage velocity resolution of the developed LDV is improved from 0.31 mm/s to 0.028 mm/s for a target withoutthe rotational velocity. The measurement results show that our new technique can offer a powerful instrument formetrology sciences.

Reflective Schmidt-Cassegrain system for largeaperturetelescopes

Mikhail Brychikhin, Nikolay Chkhalo, Yanina Eikhorn, Ilya Malyshev, Alexey Pestov, Yuri Plastinin, Vladimir Polkovnikov, Artem Rizvanov, Nikolay Salashchenko, Igor Stroulea, and Michael Toropov

Doc ID: 260658 Received 07 Mar 2016; Accepted 09 May 2016; Posted 09 May 2016  View: PDF

Abstract: A reflective modification of the Schmidt-Cassegrain system was built, tested. UV and soft X-ray applications arediscussed. The system consists of a planoid mirror with an aspheric profile, and of the prime concave andsecondary convex spherical mirrors. Spherical aberration in a wide field of view and astigmatism are compensatedby the aspheric profile of the planoid. The main parameters of the scheme are as follow: an entrance aperture of180 mm, a focal ratio F/3.2, an angular resolution better than 3" (corresponds to a pixel size of a back-sideilluminated CCD), a field of view of ±1.5° (2ω=3°) and a flat image field with a diameter of 30.4 mm. Due to theabsence of chromatic aberrations and wide field of view, the scheme is of considerable interest for thehyperspectral instruments. In particular, the operating range of the instruments can be expanded into vacuumultraviolet and ultraviolet regions.

Electro-Optic Mode Switch Based on Lithium-Niobate Mach-Zehnder Interferometer

Kaixin Chen, Mengruo Zhang, Wei Jin, and Kin Chiang

Doc ID: 262940 Received 11 Apr 2016; Accepted 09 May 2016; Posted 09 May 2016  View: PDF

Abstract: We propose an electro-optic mode switch based on an optical waveguide Mach-Zehnder interferometer fabricatedwith x-cut lithium niobate by the annealed proton-exchange process. The device can switch between thefundamental mode and the higher-order mode with a low driving voltage. Our typical fabricated device, which hasa total length of ~24 mm, shows a mode extinction ratio of ~35 dB and a 20-dB bandwidth of ~12 nm at thewavelength 1552 nm, when driven at a voltage of 1.7 V at 26 °C. High performance can be obtained at anywavelength in the C+L band with a driving voltage varying by no more than 3 V. The proposed mode switch is easyto fabricate and could find applications in reconfigurable mode-division-multiplexing systems.

87-fs Pulse Generation in a Diode-Pumped SESAM Mode-Locked Yb:YLF Laser

Federico Pirzio, Luigi Fregnani, Azzurra Volpi, Alberto Di Lieto, Mauro Tonelli, and Antonio Agnesi

Doc ID: 261662 Received 22 Mar 2016; Accepted 09 May 2016; Posted 10 May 2016  View: PDF

Abstract: An Yb:YLF crystal has been investigated in a femtosecond oscillator pumped by two 400-mW single-mode fiber-coupled diodes emitting at 976 nm and mode-locked with a SESAM. Almost Fourier transform limited pulses with duration of 87 fs and 107 fs were demonstrated for extraordinary and ordinary polarization respectively. This is, to the best of our knowledge, the first demonstration of sub-100-fs pulses with Yb:YLF and it proves the potential for ultrashort pulse generation and amplification with this material.

Inspection of disbonds in multi-layer dissimilar metalstructure using lock-in thermography

Guangkai Sun, Zhenggan Zhou, Hanxue Zhao, Pengfei He, Jin Fan, and Gen Li

Doc ID: 262255 Received 07 Apr 2016; Accepted 08 May 2016; Posted 12 May 2016  View: PDF

Abstract: This paper reports the characterization of disbonds between steel plate and lead plate on the surface of lead usinglock-in thermography. Based on the photothermal model, the excitation frequency of the bonding specimen withsteel plate and lead plate is optimized. The lock-in thermography testing system was established to inspect thespecimen. The Fourier transform method is used to process the infrared image sequences. To improve the signal tonoise ratio (SNR), fuzzy c-means (FCM) algorithm is used to process the phase matrix. The influence of clustersnumber on the processing results is researched and the optimal value of clusters number is obtained. Theshearing-phase technique is used to evaluate the size of the disbonds quantitatively. The measurement results ofthe artificial disbonds in the specimen show good agreement with the actual values. The results prove that FCM iseffective to enhance the SNR of the phase image, which makes it feasible for the quantitative determination of thedefect size by shearing-phase technique.

360-degree full-parallax light field display using panoramic camera

Haifeng Li, Chen Su, Xinxin Zhou, Qing Yang, Zhechao Wang, and Xu Liu

Doc ID: 258532 Received 29 Jan 2016; Accepted 08 May 2016; Posted 09 May 2016  View: PDF

Abstract: One of the common approaches to achieve vertical parallax for the horizontal-parallax-only light field display is to introduce the viewer-tracking method. A panoramic camera is assembled in a 360-degree scanning light field display system for the full-parallax demand in this study, wherein the image generation algorithm is improved to be sensitive to the multi-viewer positions, and the tracking and rendering are processed in real time. The horizontal-parallax-only light field display using panoramic camera is concluded to be able to achieve smooth and consecutive full-parallax performance for multiple viewers in 360-degree range.

Cat-eye effect reflected beam profiles of an optical system with sensor array

Sifeng He, Mali Gong, Wei Wang, and Rui Guo

Doc ID: 263474 Received 18 Apr 2016; Accepted 07 May 2016; Posted 09 May 2016  View: PDF

Abstract: In this paper, we propose an applicable propagation model for Gaussian beams passing through any cat-eye target instead of traditional simplification consisting of only a mirror placed at the focal plane of a lens. According to the model, the cat-eye effect of CCD cameras affected by defocus is numerically simulated. An excellent agreement of experiment results with theoretical analysis is obtained. It is found that the reflectivity distribution at the focal plane of cat-eye optical lens has great influence on the results, while the cat-eye effect reflected beam profiles of CCD cameras show obvious periodicity.

Determination of the full scattering matrix usingcoherent Fourier scatterometry

Nitish Kumar, Luca Cisotto, Sarathi Roy, Gopika Ramanandan, Silvania Pereira, and H. Urbach

Doc ID: 259285 Received 10 Feb 2016; Accepted 06 May 2016; Posted 09 May 2016  View: PDF

Abstract: We demonstrate a method to obtain the entire scattering matrix, within an arbitrary numerical aperture, ofa scatterer by using focused beam coherent Fourier scatterometry. The far field intensities of all scatteredangles within the numerical aperture of the optical system are obtained in one shot. The correspondingphases of the field are obtained by an interferometric configuration. This method enables the retrieval ofmaximum available information about the scatterer from scattered far field data contained in the givennumerical aperture of the system.

Spatially resolved scatter measurement of diffractive micromirror arrays

Cornelius Sicker, Joerg Heber, and Dirk Berndt

Doc ID: 257837 Received 09 Mar 2016; Accepted 06 May 2016; Posted 06 May 2016  View: PDF

Abstract: Spatial light modulators (SLM) support flexible system concepts in modern optics and especially phase-only SLMs such as micromirror arrays (MMA) appear attractive for many applications. In order to achieve a precise phase modulation, which is crucial for optical performance, the careful characterization and calibration of the SLM devices is required. We examine an intensity-based measurement concept, which promises distinct advantages, by means of a spatially resolved scatter measurement that is combined with the MMA’s diffractive principle. Measurements yield quantitative results, which are consistent with measurements of micromirror roughness components by white-light interferometry. They reveal relative scatter as low as 10^(-4), which corresponds to contrast ratios up to 10,000. The potential of the technique to resolve phase changes in the subnanometer range is experimentally demonstrated.

Imaging quality automated measurement of image intensifierbased on orthometric phase-shifting gratings

Yiping Cao and Song Sun

Doc ID: 258999 Received 16 Feb 2016; Accepted 05 May 2016; Posted 06 May 2016  View: PDF

Abstract: A method for automatically measuring the imaging quality parameters of image intensifier based onorthometric phase-shifting gratings (OPSG) is proposed. Two sets of phase-shifting gratings with theirfringe directions at 45° and 135° respectively are successively projected onto the input port of theimage intensifier and the corresponding deformed patterns modulated by the measured imageintensifier on its output port are captured with a CCD camera. Two phases are retrieved from these twosets of deformed patterns by a phase measuring algorithm. By building the relationship between theseretrieved phases, the referential fringe period can be figured out accurately. Meanwhile the distortedphase distribution introduced by the image intensifier can also be separated efficiently in which thesubtle imaging quality information can be further decomposed. Subsequently, the magnification of theimage intensifier is successfully measured by fringe period self-calibration. The experimental resultshave shown the feasibility of the proposed method. It can automatically measure the multiple imagingquality parameters of an image intensifier without human intervention.

Enhanced two-frequency phase-shifting method

Song Zhang and Jae-Sang Hyun

Doc ID: 261417 Received 17 Mar 2016; Accepted 05 May 2016; Posted 06 May 2016  View: PDF

Abstract: One of the major challenges of employing a two-frequency (or -wavelength) phase-shifting algorithm for absolute three-dimensional (3D) shape measurement is its sensitivity to noise. Therefore, three- for more-frequency phase-shifting algorithms are often used in lien of a two-frequency phase-shifting algorithm for applications where the noise is severe. This paper proposes a method to use geometric constraints of digital fringe projection (DFP) system to substantially reduce the noise impact by allowing the use of more than one period of equivalent phase map for temporal phase unwrapping. Experiments successfully verified the enhanced performance of the proposed method without increasing the number of patterns.

Optimization of an intraocular lens for correction ofadvanced corneal refractive errors

Staffan Schedin, Eddie Wadbro, and Per Hallberg

Doc ID: 261877 Received 24 Mar 2016; Accepted 05 May 2016; Posted 06 May 2016  View: PDF

Abstract: Based on numerical 3D ray tracing, we propose a new procedure to optimize personalized intraocular lenses (IOLs). The 3D ray tracing was based on measured corneal elevation data from patients sufferedfrom advanced keratoconus. A mathematical shape description of the posterior IOL surface, by means of a tensor product cubic Hermite spline, was implemented. The optimized lenses provide a significantly improved visual acuity for the patients. Our results include a tradeoff study that suggests that it is possible to achieve a significantly improved visual acuity with only minor perturbations from an ideal spherical lens. The proposed procedure can be applied for correction of aberrations of any optical systemby modifying a single surface.

Development of a wafer warpage measurement technique using Moiré-based method

Hung-Lin HSIEH, Yu-Hsuan Tsai, YUNG-GUANG HUANG, and Yao-Hui Huang

Doc ID: 260834 Received 17 Mar 2016; Accepted 05 May 2016; Posted 05 May 2016  View: PDF

Abstract: This paper reports on a novel technique for measuring wafer warpage, using the design concepts of moiré shift, digital moiré, autocollimator, and the scanning profiling method. The measurement system is divided into two parts: an optical moiré system and phase analysis system. The optical arrangement can be adjusted to control the projection of a linear grating image onto the surface of a wafer to be reflected back into a CCD camera. The grating image acquired by the CCD camera is used for measurement whereas a reference grating image is obtained using the digital moiré method. By overlapping the two images of the measurement and the reference gratings, the corresponding moiré fringes are formed. The phase of the moiré fringes will change proportionally to the degree of warpage in the wafer, which can be measured by detecting variations in the phase shift of the moiré fringes in the scanning profile across the surface of the entire wafer. Measurement resolution can be controlled by adjusting the pitch size of the grating or the focal length of the focusing lens, or by adjusting the angle between the images of the measurement and reference gratings. Experiment results demonstrate that the proposed method is able to achieve angular resolution of 0.2 µrad. As compared to the current warpage measurement techniques, the proposed method has the ability of high measurement resolution, high stability, and high flexibility.

Frequency difference stabilization in dual-frequency laser by stress-induced birefringence close-loop control

Jiyang Li, Yanxiong Niu, and Haisha Niu

Doc ID: 261114 Received 14 Mar 2016; Accepted 05 May 2016; Posted 05 May 2016  View: PDF

Abstract: The frequency difference of dual-frequency lasers is becoming a new research focus. The stabilization of beat frequency is of significance in fields as synthetic wavelength and shows great potential in precise measurement. In this paper, a novel device based on stress-induced birefringence close-loop control is proposed. Experiments are carried on a dual-frequency He-Ne Zeeman-birefringence laser with output mirror jointed in opposite direction. The results show that the device is capable of controlling the frequency difference variation in 1.3% in a convenient also highly cost-effective way and can increase the quantity of frequency difference, which is crucial to the application of precise measurement through dual- frequency lasers.

Relationship between the results of Laser-InducedBreakdown Spectroscopy (LIBS) and DynamicalMechanical Analysis (DMA) in composite solidpropellants during their aging

Mohammad Keshavarz, Amir Hossein Farhadian, masoud Kavosh Tehrani, Mehran Karimi, and seyyed mohammad reza darbani

Doc ID: 261572 Received 21 Mar 2016; Accepted 04 May 2016; Posted 05 May 2016  View: PDF

Abstract: Laser-induced breakdown spectroscopy (LIBS) has been used to analyze thermal aging in AP/HTPB compositesolid propellants where AP and HTPB are ammonium perchlorate and hydroxyl-terminated polybutadiene(HTPB), respectively. The method of accelerated aging was used to obtain different aged samples. DynamicalMechanical Analysis (DMA) results have been provided in order to validate LIBS results. Many methods havebeen used for accurate investigation of spectrums. First molecular bands such as CN, C2 and AlO were comparedin different samples so that their intensity ratios have been considered. In order to obtain more accuratediscrimination between different sample spectrums, Principle Component Analysis (PCA) as a suitablechemometric method has been used. All these results represent changes in the chemical structure due to timeand temperature increasing.

Range Performance of the DARPA AWARE Wide Field-of-View Visible Imager

Jonathan Nichols, Colin Olson, kyle novak, James Waterman, Steven Feller, scott mccain, Jack Anderson, David Brady, and Kyle Judd

Doc ID: 259402 Received 17 Feb 2016; Accepted 04 May 2016; Posted 04 May 2016  View: PDF

Abstract: In a prior paper, we described a new imaging architecture that addresses the need for wide field-of-view imaging combined with the resolution required to identify targets at long range. Over the last two years substantive improvements have been made to the system, both in terms of the size, weight, and power of the camera as well as to the optics and data management software. The result is an overall improvement in system performance which we demonstrate via a maritime target identification experiment.

Graphene-based fine-tunable optical delay line for optical beamforming in phased-array antennas

C. Ciminelli, Teresa Tatoli, Donato Conteduca, Francesco Dell'Olio, and Mario Armenise

Doc ID: 259871 Received 23 Feb 2016; Accepted 04 May 2016; Posted 05 May 2016  View: PDF

Abstract: The design of an integrated graphene-based fine-tunable optical delay line on silicon nitride for optical beamforming in phased-array antennas is reported. A high value of the optical delay time (τg = 920 ps) together with a compact footprint (4.15 mm2) and optical loss < 27 dB, make this device particularly suitable for a highly efficient steering in active phased-array antennas. The delay line includes two graphene-based Mach-Zehnder interferometer switches and two vertically-stacked microring resonators between which a graphene capacitor is placed. The tuning range is obtained by varying the value of the voltage applied to the graphene electrodes, which controls the optical path of the light propagation and, therefore, the delay time. The graphene provides faster reconfigurable time and low values of energy dissipation. Such significant advantages, together with negligible beam-squint effect, allow to overcome the limitations of the conventional RF beamformers. A highly efficient fine tunable optical delay line for the beam steering of 20 radiating elements up to ±20° in the azimuth direction of a tile in a phased-array antenna of an X-band SAR has been designed.

Effect of incident angle and polarization on electrically-tunable defect modes in anisotropic photonic crystals

Kazem Jamshidi-Ghaleh and Behnam Kazempour

Doc ID: 260000 Received 24 Feb 2016; Accepted 03 May 2016; Posted 03 May 2016  View: PDF

Abstract: The present study is theoretically investigated the effects of incident angle and state of wave polarization on electrically-tunable defect modes in a one-dimensional photonic crystal (1DPC) structure with an anisotropic defect layer. The 4×4 transfer matrix method is employed to calculate the transmittance spectrum of the structure with biased defect layer at different incident angles for TE and TM polarizations. The results indicate that at both polarizations, the peak wavelength of the defect mode shifts toward blue as the angle of incidence increases. Also, blue and red shifts can be observed in the defect mode for positive and negative biases, respectively. In addition, the defect mode compresses at TE(TM) polarization at negative(positive) biases and broadens for positive(negative) biases. Tunability of a defect mode has potential for the design of controllable transmission optical filters for optoelectronic devices.

Integrated label-free optical biochemical sensor withlarge measurement range based on angulargrating-microring resonator

Ma Tao, SUN LEI, Jinhui Yuan, Xinzhu Sang, Binbin Yan, Kuiru Wang, and Chongxiu Yu

Doc ID: 259979 Received 26 Feb 2016; Accepted 03 May 2016; Posted 20 May 2016  View: PDF

Abstract: We propose and design a photonic-integrated optical biochemical sensor, which comprises a microring resonatorand angular gratings in silicon-on-insulator waveguide. With the combination of the angular gratings, themeasurement range of the angular grating-microring rasonator based sensor significantly increases without therestriction of free spectral range. Optimization of the several key structural parameters is investigated to achievefavorable transmission properties. The high quality factor of more than 1.03×105 can meet the requirements ofhigh sensitivity and low detection limit. The simulation results on the biochemical bulk sensing show that theconcentration sensitivity of more than 95.27 pm/% and the detection limit of less than 0.329% can be obtained. Alarge measurement range of 50.2 nm is achieved by the combination of the angular gratings. The investigation onthe combination of microring resonator and angular grating is a valuable exploration of the liquid and gasbiomedical sensing for ultra-large measurement range.

General construction method for the rotationally symmetric ultra-short distance catadioptric projector

Feihong Yu, Zhenjie Liu, and zhenfeng zhuang

Doc ID: 261581 Received 21 Mar 2016; Accepted 29 Apr 2016; Posted 29 Apr 2016  View: PDF

Abstract: In this work, the off-axis imaging of a fan of rays with a rotationally symmetric mirror is studied, based on which, a general construction method is proposed for the rotationally symmetric ultra-short distance catadioptric projector. With the proposed method, the intermediate images in arbitrary plane of incidence can be obtained, and thus the designer has the freedom to choose suitable intermediate images to construct an initial configuration the aberration of which is small. To prove the effectiveness of the proposed method, the construction process of a convex type ultra-short distance catadioptric projector is presented, and the intermediate image in the sagittal plane is used for the initial configuration construction while the intermediate image in the meridional plane is unusable. The real performance of the convex type ultra-short distance projector is excellent.

Adaptive step size algorithm for Fourier beam propagationmethod with absorbing boundary layer of auto-determinedwidth

Eyal Feigenbaum and Ryan Learn

Doc ID: 257453 Received 13 Jan 2016; Accepted 29 Apr 2016; Posted 02 May 2016  View: PDF

Abstract: Two algorithms that enhance the utility of the absorbing boundary layer arepresented, mainly in the framework of the Fourier beam-propagation method. One isan automated boundary layer width selector that chooses a near optimal boundary sizebased on the initial beam shape. The second algorithm adjusts the propagation stepsizes based on the beam shape at the beginning of each step in order to reduce aliasingartifacts.

Lidar measurements of solid rocket propellant fireparticle plumes

David Brown, Andrea Brown, Adam Willitsford, ryan dinello-fass, Marc Airola, Karen Siegrist, Michael Thomas, and Yale Chang

Doc ID: 259325 Received 11 Feb 2016; Accepted 29 Apr 2016; Posted 02 May 2016  View: PDF

Abstract: This paper presents the first direct measurement of aerosol produced by an aluminized solid rocket propellant(SRP) fire on the ground. Such fires produce aluminum oxide particles small enough to loft high into theatmosphere and disperse over a wide area. These results can be applied to spacecraft launchpad accidents thatexpose spacecraft to such fires; during these fires, there is concern that some of the plutonium from the spacecraftpower system will be carried with the aerosols. Accident-related lofting of this material would be the net result ofmany contributing processes that are currently being evaluated. To resolve the complexity of fire processes, a selfconsistentmodel of the ground-level and upper-level parts of the plume was determined by merging ground-leveloptical measurements of the fire with lidar measurements of the aerosol plume at height during a series of SRP firetests that simulated propellant fire accident scenarios. On the basis of the measurements and model results, theJohns Hopkins University Applied Physics Laboratory (JHU/APL) team was able to estimate the amount ofaluminum oxide (alumina) lofted into the atmosphere above the fire. The quantification of this ratio is critical to acomplete understanding of the accident scenarios because contaminants are transported through the plume. Thispaper provides an estimate for the mass of alumina lofted into the air.

Anisotropic acousto-optic interaction in tellurium crystal with acoustic walk-off

Vladimir Balakshy and Andrey Voloshin

Doc ID: 261330 Received 17 Mar 2016; Accepted 29 Apr 2016; Posted 02 May 2016  View: PDF

Abstract: The influence of the acoustic beam energy walk-off on characteristics of anisotropic Bragg diffraction of light isstudied theoretically by the example of a tellurium single crystal. The calculations for wide ranges of Bragg anglesand ultrasound frequencies are produced on the basis of an original solution of acousto-optic interaction problem,which takes into consideration the acoustic walk-off. It is established that the walk-off can substantially change theregion of acousto-optic interaction, resulting in narrowing or broadening the frequency characteristic dependingon the crystal cut, acoustic frequency, incident light polarization and walk-off angle sign.

Probing ultrafast phenomena with radially polarized light

Hyunjoo Kim, Thomas Feurer, and Maryam Akbarimoosavi

Doc ID: 259947 Received 24 Feb 2016; Accepted 28 Apr 2016; Posted 29 Apr 2016  View: PDF

Abstract: A new modality for probing ultrafast phenomena which relies on radially or azimuthally polarized probe pulses is presented. First we describe the principle and then theoretically analyze the signals expected for different types of pump-induced nonlinearities. Lastly, we experimentally verify the methodology by probing a pump-induced Kerr gate with a time delayed radially polarized probe pulse. In general we find excellent agreement between the simulated and measured results.

Using maximum spectrum of continuous wavelet transform for demodulation of overlapping spectrum in FBG sensor network

Ying Hu, Wenqin Mo, KAIFENG DONG, Junlei Song, and Fang Jin

Doc ID: 259483 Received 29 Feb 2016; Accepted 28 Apr 2016; Posted 17 May 2016  View: PDF

Abstract: Maximum spectrum of continuous wavelet transform(MSCWT) was proposed to demodulate the central wavelengths of the overlapped spectrum in the serial fiber Bragg grating(FBG) sensor system. We described the operation principle of MSCWT method. Moreover, the influence of the interval gap between two FBGs wavelength, 3dB-bandwidth and optical power of the reflected spectrum were discussed. The simulation and experimental results indicated that MSCWT could resolve an overlapped spectrum and decode the central wavelength with high accuracy. More importantly, the proposed peak detection method could enhance the sensing capacity of the WDM-FBG sensor network.

Ultra-sensitive, real-time trace gas detection using a high-power, multi-mode diode laser and cavity ringdown spectroscopy

Gottipaty Rao, Andreas Karpf, and Yuhao Qiao

Doc ID: 259220 Received 16 Feb 2016; Accepted 26 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: We present a simplified Cavity Ring-down (CRD) trace gas detection technique that is insensitive to vibration, andcapable of extremely sensitive, real-time absorption measurements. A high power, multi-mode Fabry-Perot (FP)diode laser with a broad wavelength range (Δλ_laser ~ 0. 6 nm) is used to excite a large number of cavity modes,thereby reducing the detector’s susceptibility to vibration and making it well suited for field deployment. Whendetecting molecular species with broad absorption features (Δλ_absorption » Δλ_laser), the laser’s broad linewidthremoves the need for precision wavelength stabilization. The laser’s power and broad linewidth allow the use ofon-axis cavity alignment, improving the signal-noise-ratio while maintaining its vibration insensitivity. The use ofa FP diode laser has the added advantage of being inexpensive, compact and insensitive to vibration. Thetechnique was demonstrated using a 1.1 Watt (λ = 400 nm) diode laser to measure low concentrations of NitrogenDioxide (NO2) in zero air. A sensitivity of 38 parts-per-trillion (ppt) was achieved using an integration time of 128ms; for single-shot detection, 530 ppt sensitivity was demonstrated with a measurement time of 60 μs which opensthe door to sensitive measurements with extremely high temporal resolution; to the best of our knowledge, theseare the highest speed measurements of NO2 concentration using CRDS. The apparatus’ reduced susceptibility tovibration was demonstrated by introducing small vibrations into the apparatus and observing that there was nomeasurable effect on the sensitivity of detection.

Wavelength Optimization Using Available Laser Diodes in Spectral Near-infrared Optical Tomography

Min-Chun Pan, MIN-CHENG PAN, Liang-Yu Chen, and CHUNG-CHEN YAN

Doc ID: 260272 Received 01 Mar 2016; Accepted 25 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: As employing optimized wavelengths, a near-infrared (NIR) tomographic imaging system with multi-wavelengths in continuous wave (CW) enables to provide accurate information of chromophores. In this paper, we discuss wavelength optimization with the selection from commercial laser diodes. Through theoretical analysis, we use the residual norm (R) and the condition number (κ) to represent the uniqueness of a matrix problem and the smooth singular-value distribution of each chromophore, respectively. The optimum wavelengths take place for large R and small κ. We considered totally 38 wavelengths of laser diodes in the range of 633-980 nm commercially available to discover optimum sets for a broad range of chromophore combinations. In the total 38 wavelengths, there exist 501,942 (C385), 2,760,681 (C386), and 12,620,256 (C387) combinations of five, six, and seven wavelength sets, respectively, for accurately estimating chromophores (HbO2, HbR, H2O, and lipid), water, lipid plus the scattering prefactor A. With the numerical calculation, top 10 wavelength sets were selected based on the principle of large R and small κ. In the study, the chromophore concentration for young and old women are investigated; finally, choosing the laser diodes with the wavelength of 650, 690, 705, 730, 870/880, 915 and 937 nm is recommended either for young or old women to construct a spectral NIR tomographic imaging system in the CW domain.

INVERSION METHOD BASED ON STOCHASTIC OPTIMIZATION FOR PARTICLE SIZING

Juan Sánchez-Escobar, Liliana Ibeth Santillan, Javier Vargas Ubera, and J.Felix Aguilar

Doc ID: 258454 Received 29 Jan 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: A stochastic inverse method is presented based on a hybrid evolutionary optimization algorithm (HEOA) to retrieve a particle-size distribution (PSD) from the angular distribution of scattered light. By solving an optimization problem, the HEOA (with the Fraunhofer approximation) retrieves the PSD from an intensity pattern generated by Mie theory. The analyzed light-scattering pattern can be attributed to unimodal normal, gamma, or lognormal distribution of spherical particles covering the interval of modal size parameters The HEOA ensures convergence to the near-optimal solution during the optimization of a real-valued objective function by combining the advantages of both a multi-member evolution strategy (MMES) and locally weighted linear regression (LWLR). The numerical results show that our HEOA can be satisfactorily applied to solve the inverse light-scattering problem avoiding the use of a priori information about the domain of the sought distribution.

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