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Accepted papers to appear in an upcoming issue

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Generation of High-Average Power, Ultra-Broadband, Infrared Radiation

Zachary Epstein, B. Hafizi, Joseph Penano, and Phillip Sprangle

Doc ID: 340476 Received 24 Jul 2018; Accepted 17 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: High-average power, ultra-broadband, mid-IR radiation can be generated by illuminating a nonlinear medium with a multi-line laser radiation. Propagation of a multi-line, pulsed CO2 laser beam in a nonlinear medium, e.g. gallium arsenide or chalcogenide, can generate directed, broadband, IR radiation in the atmospheric window (2 – 13 µm). A 3-D laser code for propagation in a nonlinear medium has been developed to incorporate extreme spectral broadening resulting from the beating of several wavelengths. The code has the capability to treat coupled forward and backward propagating waves, as well as transverse and full linear dispersion effects. Methods for enhancing the spectral broadening are proposed and analyzed. Grading the refractive index radially or using a cladding will tend to guide the CO2 radiation and extend the interaction distance, allowing for enhanced spectral broadening. Nonlinear coupling of the CO2 laser beam to a backwards-propagating, reflected beam can increase the rate of spectral broadening in the anomalous dispersion regime of a medium. Laser phase noise associated with the finite CO2 linewidths can significantly enhance the spectral broadening as well. In a dispersive medium laser phase noise results in laser intensity fluctuations. These intensity fluctuations result in spectral broadening due to the self-phase modulation mechanism. Finally, we present propagation through a chalcogenide fiber as an alternative for extreme spectral broadening of a frequency-doubled CO2 multi-line laser beam.

Computational Analysis of Dispersive and Nonlinear 2D Materials by Using a Novel GS-FDTD Method

Jian Wei You, Nicolae Panoiu, Edward Threlfall, and Dominic Gallagher

Doc ID: 336150 Received 29 Jun 2018; Accepted 16 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: In this paper, we propose a novel numerical method for modeling nanostructures containing dispersive and nonlinear two-dimensional (2D) materials, by incorporating a nonlinear generalized source (GS) into the finite-difference time-domain (FDTD) method. Starting from the expressions of nonlinear currents characterizing nonlinear processes in 2D materials, such as second- and third-harmonic generation, we prove that the nonlinear response of such nanostructures can be rigorously determined using two linear simulations. In the first simulation, one computes the linear response of the system upon its excitation by a pulsed incoming wave, whereas in the second one the system is excited by a nonlinear generalized source, which is determined by the linear near-field calculated in the first linear simulation. This new method is particularly suitable for the analysis of dispersive and nonlinear 2D materials, such as graphene and transition-metal dichalcogenides, chiefly because, unlike the case of most alternative approaches, it does not require the thickness of the 2D material. In order to investigate the accuracy of the proposed GS-FDTD method and illustrate its versatility, the linear and nonlinear response of graphene gratings have been calculated and compared to results obtained using alternative methods. Importantly, the proposed GS-FDTD can be extended to 3D bulk nonlinearities, rendering it a powerful tool for the design and analysis of more complicated nanodevices.

Generation of millijoule few-cycle pulses at 5 µm by indirect spectral shaping of the idler in an OPCPA

Uwe Griebner, Martin Bock, Lorenz von Grafenstein, and Thomas Elsaesser

Doc ID: 338698 Received 12 Jul 2018; Accepted 16 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: Spectral pulse shaping in a high-intensity midwave-infrared (MWIR) optical parametric chirped pulse amplifier (OPCPA) operating at 1 kHz repetition rate is reported. We successfully apply a MWIR spatial light modulator (SLM) for the generation of ultrashort idler pulses at 5 µm wavelength. Only bulk optics and active phase control of the 3.5 µm signal pulses via the SLM are employed for generating compressed idler pulses with a duration of 80 fs. The 80 fs pulse duration corresponds to less than five optical cycles at the central wavelength of 5.0 µm. The pulse energy amounts to 1.0 mJ which translates into a peak power of 10 GW. The generated pulse parameters represent record values for high-intensity midwave-IR OPCPAs.

Bubble dynamics driven by few successive femtosecond laser pulses in methanol under 1 kHz

Qi PengFei, Qiang Su, Lie Lin, and Weiwei Liu

Doc ID: 340549 Received 24 Jul 2018; Accepted 14 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: The breakdown and related bubble dynamics driven by femtosecond laser pulses in liquid are very critical for the optimization of laser parameters in the applications of medical laser and nano/micro objects manipulation. In this letter, we conduct a systematical research on the bubble dynamics in methanol driven by few successive femtosecond laser pulses under 1 kHz repetition rate. It is demonstrated that it is more probably for two or more successive pulses to induce optical breakdown than single pulse only. A physical scenario of bubble dynamics from generation to evolution is presented for the successive femtosecond laser pulses interacting with sample, which also give a reasonable explanation for such phenomenon. Moreover, the effects of pulse energy and numerical aperture on the optical breakdown and bubble dynamics are investigated and well explained. It hints that the laser pulses with high repetition rate and low energy and the lens with large numerical aperture may be an optimal choice for the precise control of bubble and cutting.

Ghost Surface Phononic Polaritons

Sheng Zhou, Qiang Zhang, shufang fu, and Xuan-Zhang Wang

Doc ID: 332320 Received 24 May 2018; Accepted 14 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: Three ghost surface phonon polaritons (ghost SPhPs) and one ghost evanescent wave were predicated at the single oblique surface of layered ionic-crystal metamaterial (ICMM). They propagate along the surface but their electromagnetic fields in the ICMM sinusoidally oscillate and exponentially attenuate with the distance from the surface. The three ghost SPhPs are mutually different in character. Two among them are situated in two different frequency ranges respectively wherein the ICMM is a hyperbolic material and the other lies in the frequency region where the ICMM is an elliptical material. The ghost evanescent wave is very special. Its characters are: (1) Its energy can only conduct outside the ICMM; (2) Its wave vector and electric field possess the same direction transverse to the material optical axis. The conditions for the existence of the ghost SPhPs were discussed. The numerical results were obtained based on ZnS/SiO2 metamaterials.

Effect of Dispersion on Sensing Parameters of a Racetrack Resonator Based Biosensor at 850 nm

foroogh khozeymeh and Mohammad Razaghi

Doc ID: 335492 Received 20 Jun 2018; Accepted 11 Sep 2018; Posted 13 Sep 2018  View: PDF

Abstract: In this paper, the effect of dispersion on sensing parameters of a racetrack resonator based biosensor is studied. It is shown that dispersion has a significant effect in biosensing characteristics of a ring resonator designed with silicon-oxy-nitride (SiON) waveguides in racetrack configuration. Based on the results, high sensitivity (S) can be achieved using SiON race track resonator as a biosensing device. Simultaneously, this device has a high total quality factor (Q_t). The highest S for transverse electric whispering gallery mode resonance (TE WGM Res.) of 1 (2), is found to be 84.80 (403.34) nm/RIU at optimized ring radii of 89-90 μm (29-30μm). At the same time, the highest Q_t factor of ~4.6*10^4 is obtained for TE WGM Res. of 1 and 2, at biological cladding. These amounts of S and Q_t factor, resulting in an ultra-high figure-of-merit (FOM) of 4613 RIU^-1 and 22216 RIU^-1 respectively for TE WGM Res. 1 and 2. Based on the FOM calculations, our sensor structure performs 220 order of magnitude better than surface plasmon resonance (SPR) devices for bulk refractometric sensing. Device analysis is done by the simple, fast and reliable analytically methods. The model results are validated through comparisons with experimental reports.

Numerical analysis of high-Q multiple Fano resonances

Wan-Ying Li, qi lin, Lingling Wang, and Xiang Zhai

Doc ID: 337801 Received 03 Jul 2018; Accepted 10 Sep 2018; Posted 13 Sep 2018  View: PDF

Abstract: We design and numerically analyze high-Q multiple Fano resonances based on a hybrid metamaterial waveguide (HMW) structure, which consists of T-shaped gold cut wires placed on dielectric board waveguide. There are three sharp Fano peaks arising from the interference between plasmon dipole mode and different guided modes. The physical origin of obvious Fano behaviors is explained by the three-level plasmonic system and slab waveguide theory. The largest Q-factor reaches 547, and modulation depth of the peak C can get nearly 100%, which can perfectly realize Fano switch function. Combining the cramped spectral lines with large near-field confinement, we demonstrate an optical refractive index sensor with a sensitivity of 4920 nm/RIU and a figure of merit of 188. This work provides a way to obtain multiple high Q-factor Fano resonances, which can widen channels for fabricating device in biochemical sensing, optical switching.

Tuning hyper-Rayleigh scattering amplitude on magnetic colloids by means of external magnetic field

Eduardo Gonçalves, Ruben Fonseca Rodriguez, Leonardo De Boni, and Antonio Martins Figueiredo Neto

Doc ID: 331038 Received 07 May 2018; Accepted 09 Sep 2018; Posted 10 Sep 2018  View: PDF

Abstract: The first-order hyperpolarizability β of magnetite nanoparticles in colloidal dispersion was measured in the presence and absence of external magnetic field of magnitude H = 800 G, applied with permanent neodymium magnets. For that, the (linear) attenuation spectrum was measured and the nonlinear properties were obtained through the hyper-Rayleigh scattering technique. The attenuation spectrum is the same regardless the external magnetic field, indicating that large aggregates of nanoparticles were not formed on our system. The first hyperpolarizability, on the other hand, increased when the incident beam polarization was parallel to the magnetic field lines and decreased when the directions were orthogonal, due to the alignment of crystallographic planes of the material when nanoparticles rotate in order to align their individual magnetic momentum with respect the external field. In the absence of magnetic field, the hyperpolarizability β(H=0) = 8.5(1) × 10¯²⁸ cm⁵/esu. For the parallel case, β(||)=9.8(2) × 10¯²⁸ cm⁵/esu, while for the perpendicular configuration, β(⊥)=8.1(1) × 10¯²⁸ cm⁵/esu. Defining the x-axis of the particle reference frame parallel to the <111> crystallographic direction, which corresponds to the direction of easy magnetization, β(||)=βxxx, and β(⊥) corresponds to a average from βyyy and βzzz. When there's no external field applied, the nanoparticles are randomly oriented and the measured hyperpolarizability corresponds to an average over the three orthogonal directions, that is, <β(H)> = 1/3[β(||)+2β(⊥)] = 8.6 × 10¯²⁸ cm⁵/esu, which is compatible with the measured value for the system without magnetic field β(H=0).

Weak scattering of Multi-Gaussian Schell-model vortex beams on a deterministic medium

YuanYuan Zhang and Jianyang Zhou

Doc ID: 331575 Received 14 May 2018; Accepted 09 Sep 2018; Posted 10 Sep 2018  View: PDF

Abstract: The scattering of a multi-Gaussian Schell-model (MGSM) vortex beam upon a deterministic medium is investigated within the accuracy of the first-order Born approximation. The explicit expression for the cross-spectral density function of the far-zone scattered field is derived and some numerical examples are given to show the dependences of the spectral density, spectral degree of coherence on the source parameters and the scatterer parameter. It is found that by adjusting these parameters (especially the transverse coherence width of the source) we can shape the scattered beam profile into quasi-Gaussian, flat-topped or subsidence structure. Besides, for the distributions of the modulus of the spectral degree of coherence, secondary maxima occur when the incident beam is a vortex beam.

Visible Aluminum Monoxide Emission during Long Pulse mid-Infrared Ablation of Aluminum in Air

Todd Van Woerkom, Glen Perram, Brian Dolasinski, Patrick Berry, and Charles Phelps

Doc ID: 332515 Received 24 May 2018; Accepted 07 Sep 2018; Posted 10 Sep 2018  View: PDF

Abstract: The long pulse ablation of aluminum wafers in ambient air using an Er:YAG laser at 2.94 μm wavelength is presented. Visible emission spectra collected during ablation are assigned to the B²Σ+ → X²Σ+ molecular electronic transition of aluminum monoxide (AlO). A rovibronic model including self-absorption within the plume is developed to determine the molecular temperature. A 60. μs pulse at a fluence of 249.92 ± 40 J/cm², a temperature of 2843 ± 32 K and 3013 ± 30 K were found with the linear and nonlinear models, respectively. A greybody background, with an emissivity of approximately 1.3E-6 was observed, implying a low volume mixing fraction of particulates in the plume. A linear fit of the ∆v = −1 sequence was developed to rapidly analyze hundreds of spectra taken as a background pressure was varied from 400 mbar to 1000 mbar. The AlO temperature is approximately independent of background pressure. Finally, comparisons to other laser ablation studies at shorter wavelengths and shorter pulse durations are made wherever possible.

Modulation Transfer Spectroscopy for D1 transition line of Rubidium

Bin Wu, Yin Zhou, Kan Weng, Dong Zhu, Zhi Fu, Bing Cheng, Xiaolong WANG, and Qiang Lin

Doc ID: 332698 Received 04 Jun 2018; Accepted 07 Sep 2018; Posted 10 Sep 2018  View: PDF

Abstract: The modulation transfer spectroscopy (MTS) is widely used in optical laboratory for laser frequency stabilization. There have been many theoretical and experimental papers on this spectroscopic method. However, most of the works focus on the cycling transitions like the D2 line of rubidium. In this paper, the modulation transfer spectroscopy for non-cycling transitions is investigated. We consider D1 line of rubidium whose modulation transfer spectrum has been determined and compared with the polarization spectrum. It is found that the slope of the modulation transfer signal is sharper than the polarization spectrum. The dependence of signal amplitude on the temperature of vapor cell was analyzed, and the high signal-to-noise-ratio spectra are achieved for D1 open transitions. The obtained results provide an effective spectroscopic method for the robust frequency locking of laser at a wavelength of 795nm.

Mode coupling and competition in square-racetrack hybrid-cavity semiconductor lasers

Yue-De Yang, yong-Heng zhang, Hai-Zhong Weng, Jin-Long Xiao, and Yong-Zhen Huang

Doc ID: 340949 Received 30 Jul 2018; Accepted 06 Sep 2018; Posted 10 Sep 2018  View: PDF

Abstract: We propose and demonstrate square-racetrack hybrid-cavity semiconductor lasers to achieve lasing mode control. Strong mode coupling between the whispering-gallery modes of the square and racetrack cavities is predicted by the finite element method numerical simulation and confirmed by the experimental lasing spectra. The mode coupling leads to the anti-crossing of the mode wavelengths, the crossing of the mode quality factors, and the hybrid modes with the field distributing in both the square and racetrack cavities, and will affect the competition of lasing modes together with the gain distribution induced by the separately injected current of the two cavities. Single-mode lasing with a side-mode suppression-ratio up to 38 dB and dual-mode lasing with an intensity ratio down to 1 dB are realized by tuning the injection current. Furthermore, increasing racetrack cavity size changes the mode competition process and results in racetrack-mode-dominated lasing for the square-racetrack hybrid-cavity semiconductor lasers.

Theoretical investigation of the capture effect inIMDD-based microwave photonic mixers

S.Esmail Hosseini and M. Mahdi Keshavarz

Doc ID: 332276 Received 21 May 2018; Accepted 04 Sep 2018; Posted 04 Sep 2018  View: PDF

Abstract: We study the large-signal behavior of microwave photonic (MWP) mixers to investigate the small-signal suppression phenomenon commonly referred to as the capture effect. We introduce and theoretically study the capture effect in the context of MWP mixers. Theoretical expressions are derived for calculatingthe capture effect in three basicMWPmixer types based on intensity-modulation direct-detection (IMDD). We show that the capture effect is not only a function of the power ratio between the input radio-frequency (RF) signals to the MWP mixers, but also depends on the absolute value of their powers. We extendthe study to different unequal-power frequency components of a signal, and as a practical example, we investigate the capture effect when a narrowband FM signal is applied to the RF input of an IMDD-based MWP mixer, theoretically demonstrating considerations and limitations in using MWP mixers.

Wavelength beam combining by spectrally selective polarization transformation

Matvey Pochechuev, Anastasia Suvorina, Pavel Shcheglov, Sergei Nikitin, and Aleksei Zheltikov

Doc ID: 335768 Received 21 Jun 2018; Accepted 04 Sep 2018; Posted 04 Sep 2018  View: PDF

Abstract: Efficient wavelength beam combining is demonstrated using spectrally selective polarization transformation in carefully designed stacks of birefringent plates combined with polarization-selective beam splitters. This beam-combining scheme is shown to enable a high-throughput power and intensity scaling of blue-diode-laser arrays. The wavelengths of individual diode lasers in the laser array are shifted with respect to each other by a few nanometers, by fine temperature adjustment, for the highest overall output radiance, limited by étendue conservation.

Realizing Gauss hypergeometric beam described as $_2F_1(a,b,c;x^2)$ by Bessel-spiral zone plate

Arash Sabatyan and Seyyed Mojtaba Taheri

Doc ID: 332942 Received 31 May 2018; Accepted 04 Sep 2018; Posted 05 Sep 2018  View: PDF

Abstract: Apodizing spiral zone plate with Bessel functions shows interesting focusing behavior in a generation a variety of-of uni and multiannular (specially biannular), azimuthal and annular vortex beam carrying screw and annular phase dislocation.Theoretically studies utilizing scalar diffraction integral show generation of hypergeometric $_2F_1(a,b,c;x^2)$ beams. Then, considering two important parameters including the order of the Bessel functions and topological charge, their impacts, and roles in the features of the generated focused beams are examined. Simulation and experimental results are in a very good agreement together.

Utilizing a circular stop at the back focal plane of the objective optimizes the maximum linear and maximum applicable axial forces of optical tweezers

Nader Reihani, hossein gorjizadeh, and Sajad Meydanloo

Doc ID: 336239 Received 27 Jun 2018; Accepted 03 Sep 2018; Posted 04 Sep 2018  View: PDF

Abstract: Optical tweezers are indispensable force-spectroscopes. The trap stiffness and the linear force range of the instrument determine theworking force range of the instrument. Herewe showboth theoretically and experimentally that utilizing a circular obstruction at the back focal plane of the objective can significantly increase the maximum linear force. For instance, utilizing a disk with an obstruction ratio of 0.773 could increase themaximumlinear force by a factor of ∼ 39 when a 3.4 μm polystyrene bead is trapped. We also show that this simple beamshapingmethod can significantly improve the maximum applicable force per unit power of the laser entring the objective lens.

Quantum model for traveling-wave electro-optical phase modulator

Dmitri Horoshko, Mahdi Eskandary, and Sergei Kilin

Doc ID: 341165 Received 30 Jul 2018; Accepted 03 Sep 2018; Posted 17 Sep 2018  View: PDF

Abstract: We develop a quantum model of traveling-wave electrooptical phase modulator by considering a parametric interaction of the optical and the radiofrequency waves in the modulator medium by means of the electro-optic effect. The model includes a possible dispersion of the modulator medium in the optical domain. In the case of negligible dispersion we derive a simple analytic expression for the evolution operator of the optical field, which has been proposed previously in the literature on the basis of an analogy to the classical field transformation. We study by means of a perturbative approach the influence of small dispersion on the field evolution operator and formulate conditions of negligibility of modulator dispersion. We demonstrate the signature of dispersion in phase modulation: breaking the symmetry of sidebands with respect to the mean photon number. We obtain the law of transformation of a multimode coherent state by a phase modulator, which is important for understanding the structure of signal states in quantum cryptographic schemes utilizing phase modulation of coherent optical beams.

A comprehensive study of the transitions between stable mode locking and soliton explosions in a fiber laser mode-locked with nonlinear amplifying loop mirror

Sahar Hajizadeh Nazari and Atoosa Arabanian

Doc ID: 337877 Received 06 Jul 2018; Accepted 31 Aug 2018; Posted 04 Sep 2018  View: PDF

Abstract: We present a comprehensive study on dynamic of transitions between stable mode locking and instabilities with soliton explosions or noise-like emissions depending on all of the effective parameters of the fiber laser cavity mode locked by nonlinear amplifying loop mirror (NALM). By numerical solving of a generalized nonlinear Schrodinger equation, the spectral and temporal shapes of the pulses during the different roundtrips are calculated and the event of soliton explosions is investigated by tuning characteristic of components of the cavity such as components in the main loop, i.e, filter bandwidth, the length of passive fiber, the rate of output coupling, and pump power, and also, the components of NALM, i.e, its pump power, its passive fiber length and the coupling rate of this loop to the main loop. We found that how by tuning of each parameter and adjusting the nonlinear phase difference of clockwise and counterclockwise waves in the NALM, one can convert an unstable state with the soliton explosions to a long-term stable mode locking state.

Thermally deformable mirror to compensate for phase aberrations in high-power laser systems

Elke Schmid and Peter Mahnke

Doc ID: 335351 Received 15 Jun 2018; Accepted 31 Aug 2018; Posted 04 Sep 2018  View: PDF

Abstract: We report on a thermally deformable mirror to compensate for aberrations in high-power laser systems, suitable for intra-cavity as well as extra-cavity implementations in laser oscillators and laser amplifiers. The adaptive mirror consists of a thin polished edge filter which is mounted on a heat sink. Local deformations of the adaptive mirror are yield by absorbing the emission of a so-called "heating laser" in the rear-side cooled mirror substrate. Thus, imaging suitable intensity profiles on the mirror enable to perform laterally highly-resolved profiles of optical path differences (OPD) to compensate systematically for phase aberrations. For this, a Digital Light Processing (DLP) micro mirror array of a commercial projector, irradiated by a top hat shaped "heating beam" is mapped on the adaptive mirror. Achievable deformations of the adaptive mirror have been measured using a Shack-Hartmann wavefront sensor. A high lateral resolution of 0.1 μm/mm radius and an maximal OPD of 0.569 μm could be demonstrated successfully.

Hybrid method of plane-wave and cylindrical-wave expansions for distributed Bragg-reflector pillars: formalism and its application to topological photonics

Tetsuyuki Ochiai

Doc ID: 328904 Received 19 Apr 2018; Accepted 30 Aug 2018; Posted 30 Aug 2018  View: PDF

Abstract: A hybrid computational method of plane-wave and cylindrical-wave expansions for distributed Bragg-reflector (DBR) pillars is proposed. The plane-wave expansion is employed to represent the one-dimensional periodic structure of the DBR. The cylindrical-wave expansion is employed to describe the scattering by circular pillars with the DRB structure inside. This formalism enables us to investigate optical properties of isolated and arrayed DBR pillars, particularly, their photonic band structures and optical transport spectra. Using this formalism, we present a novel formation of gapless Dirac-cone surface states in a three-dimensional photonic crystal composed of a two-dimensional periodic arrangement of coaxial DBR pillars.

Tunable hyperbolic photonic devices

Susobhan Das, Alessandro Salandrino, and Rongqing Hui

Doc ID: 332977 Received 31 May 2018; Accepted 28 Aug 2018; Posted 29 Aug 2018  View: PDF

Abstract: One of the unique characteristics of hyperbolic metamaterials (MM) is the possibility of accessing various regimes of extreme anisotropy. Here, we propose a MM based on periodic layers of hafnium oxide (HfO2) and mono-layer graphene. Taking advantage of the fact that the permittivity of graphene can be controlled by changing its chemical potential via an externally applied voltage, we theoretically investigate the anisotropic behavior of the proposed MM as a function of the external electrical bias. Based on our findings we provide examples of possible nanophotonic device applications exploiting such tunable hyperbolic MM. Prototypes of polarizer, modulator and MM assisted tunable coupler are investigated at the 1550nm communication’s wavelength. Additionally, we show that the high tuning efficiency of MM allows miniaturized device to be realized with enhanced functionality-per-area for photonic integration.

SOA-fibre laser mode-locked by gain modulation

Sergey Kobtsev, Boris Nyushkov, Konstantin komarov, Andrey Komarov, and Alexander Dmitriev

Doc ID: 340909 Received 27 Jul 2018; Accepted 28 Aug 2018; Posted 29 Aug 2018  View: PDF

Abstract: This work reports for the first time on experimental and theoretical study of mode locking via synchronous pumping of a semiconductor optical amplifier (SOA) used as the active medium of a fibre laser. SOA modulation with injection current pulses having duration of 1.2 µs and repetition rate equal to that of the fundamental inter-mode frequency spacing of the cavity (84.9 kHz) led to generation of mode-locked pulses with duration of 650 ns at a wavelength of 1.54 µm. Feasibility of the proposed method and the basic parameters of the generated pulses are corroborated by numerical modelling. The key advantages of the proposed laser are simplicity of implementation, comparatively high efficiency, spectral universality, and possibility of pulse shape control.

Modeling of XUV-induced damage in Ru films: the role of model parameters

Igor Milov, Vladimir Lipp, Nikita Medvedev, Igor Makhotkin, Eric Louis, and Fred Bijkerk

Doc ID: 334228 Received 04 Jun 2018; Accepted 27 Aug 2018; Posted 28 Aug 2018  View: PDF

Abstract: We perform a computational study of damage formation in XUV-irradiated ruthenium thin films by means of a combined Monte Carlo – two temperature model approach. The model predicts that the damage formation is most affected by ultrafast heating of the lattice by hot electrons, and is not very sensitive to the initial stage of the material excitation. Numerical parameters of the model, as well as different approximations for the thermal parameters were analyzed, showing the importance of the temperature dependence of the electron thermal conductivity and the electron-phonon coupling factor. Our analysis reveals that the details of photoabsorption and ultrafast non-equilibrium electron kinetics play only a minor role in the XUV irradiation regime.

Novel multiple transparency in a multimode quadratic coupling ptomechanical system with an ensemble of three-level atoms

Guo Ge, Qing He, Fazal Badshah, Rafi Din, Haiyang Zhang, and Yong Hu

Doc ID: 334586 Received 06 Jun 2018; Accepted 26 Aug 2018; Posted 27 Aug 2018  View: PDF

Abstract: We theoretically consider novel multiple transparency in a multimode quadratic coupling optomechanical system (OMS) assisted with N cold Λ-type three-level atoms. The coupling interaction between the two mechanical membranes (MR1 and MR2) and the cavity is quadratic. The three-level atoms interact with an external controlling field and an internal cavity field. The optical cavity is driven by a strong coupling field and a weak probe field. In the resolved sideband regime, there appears the four transparent windows resulted from atomic coherence and quadratic coupling in the absorption spectrum by using suitable parameters. We study how to switch the number of transparent dips between the two, threeand four transparent dips, and adjust spacing between two transparent dips by changing the controlling parameters, including the strength of the quadratic coupling between MR1 (MR2) and the cavity, the collective coupling strength between the atomic ensemble and the cavity field, the Rabi frequency associated with the coupling interaction between the controlling field and the three-level atom, and power of the coupling field. Further, We also demonstrate the normal-mode splitting in the generated Stokes and anti-Stokes field in the OMS, where the change of the collective coupling strength can affect the splitting width of the output field at the Stokes (anti-Stokes) frequency.

Sensing and characterization of bisphenol ‘AF’ with mid-infrared spectroscopy and searching the commonality among bisphenol ‘A’, ‘S’ and ‘AF’

Ramzan Ullah and Xiangzhao Wang

Doc ID: 331906 Received 21 May 2018; Accepted 26 Aug 2018; Posted 30 Aug 2018  View: PDF

Abstract: Mid-infrared spectroscopy (400 cm-1 to 4000 cm-1) of Bisphenol ‘AF’ is manifested. Bisphenol ‘AF’ is another variant of Bisphenol ‘A,’ besides Bisphenol ‘S’. Bisphenol ‘A’ is being curbed due to its malign effects. Bisphenol ‘AF’ is gradually taking the place of Bisphenol ‘A.’ Bisphenol ‘AF’ tends to have malignancy equal or more than Bisphenol ‘A.’ Molecular vibrations of Bisphenol ‘AF’ have been observed by mid-infrared spectroscopy and analyzed by Density Functional Theory calculations for possible countermeasure. Principal Component Analysis is used on detected absorption frequencies of Bisphenol ‘AF’ in conjunction with prior reported frequencies of Bisphenol ‘A’ and ‘S’ in the mid-infrared range. List of correlating absorption frequencies of bisphenol ‘A,’ ‘S’ and ‘AF in the mid-infrared range is populated. This correlation may lead to group such toxic materials and to find the origin of toxicity by knowing the nature of correlated vibrations and related involvement of functional groups and atoms.

Sub-optical wavelength Localization of Rydberg superatoms

Rahmat Ullah, Zia uddin, YOU-LIN CHUANG, Ray-Kuang Lee, and Sajid Qamar

Doc ID: 331527 Received 11 May 2018; Accepted 24 Aug 2018; Posted 29 Aug 2018  View: PDF

Abstract: With the interaction among one optical probe field and pairs of standing microwaves in the configuration of Rydberg-dressed electromagnetically induced transparency, we study theoretically the sub-wavelength localization of Rydberg superatoms in two- and three-dimensions. Composited by an ensemble of Rydberg atoms with strong dipole-dipole interactions, a superatom can be localized within the optical wavelength through the position-dependent atom-field interaction. By measuring the absorption spectrum from the optical probe field, a single position of Rydberg superatoms with high precision can be obtained, depending on the probe field detuning and phase shifts associated with the standing microwaves.

Tunable polarization converter based on one-Dimensional graphene metasurfaces

Amin Khavasi, Mohammad Reza Tavakol, and Babak Rahmani

Doc ID: 334832 Received 11 Jun 2018; Accepted 24 Aug 2018; Posted 24 Aug 2018  View: PDF

Abstract: We introduce a new metasurface structure for controlling the polarization of light by leveraging the well-harmonized combination of graphene and dielectric. The proposed metasurface is composed of an array of rectangular pillars laterally sandwiched by ribbons of graphene. Being able to dynamically change the polarization state of the reflected wave, the proposed structure is employed to realize a switchable polarization converter which is able to act as a reflector (co-polarizer)/RHC quarter-wave plate or RHC/cross/LHC polarizer based on its design configuration. The reflected amplitude in all states of functionality is remarkably high. It is also shown that for some states, the proposed polarization converter demonstrates broad working bandwidth both spatially and spectrally. Therefore, it could find applications in Terahertz imaging, sensing and communication and also could be easily used to realize other beam shaping functionalities such as lensing.

General method of passive optical pulse peak intensitystabilization through controlled self-phase modulationand over-compression

Alexandr Špaček, Jonathan Green, Frantisek Batysta, Jakub Novák, Roman Antipenkov, Pavel Bakule, and Bedrich Rus

Doc ID: 337945 Received 06 Jul 2018; Accepted 23 Aug 2018; Posted 24 Aug 2018  View: PDF

Abstract: A method of peak intensity stabilization of opticalpulses is presented which is based on the combinationof self-phase modulation (SPM) and an optical compressor.Spectral broadening via SPM can occur forintense laser pulses propagating through a nonlinearmedium. For Gaussian pulses, this nonlinear broadeningresults in a nonlinear spectral phase which positivelychirps the pulse. Because this is a nonlinearprocess, the amount of spectral broadening depends onthe intensity of the laser pulse with increased broadeningfor higher intensities. Here we propose a techniqueof peak intensity stabilization by accumulating amodest amount of nonlinear spectral phase on a pulsevia SPM and subsequently introducing a negative netGDD with an optical compressor. For the appropriatevalue of compressor GDD, the energy dependent chirpis balanced such that the peak intensity of the pulseis stabilized. Simulations of this method for realisticpulse parameters predict an increase in peak intensitystability by well over an order of magnitude.

Visibility Minimization of the Moiré Pattern on the display screen by optimizing geometrical parameters using F/θ-plot

NanEi Yu, Victor Yurlov, Tae Young Kim, Kyunghun Han, Young-Joo Kim, and marzieh pournoury

Doc ID: 338549 Received 11 Jul 2018; Accepted 23 Aug 2018; Posted 24 Aug 2018  View: PDF

Abstract: This paper discusses the visibility issue of the moiré pattern, which may appear on the display screen as a result of the interference between screen pixel array and other periodical structures having size of pitch close to the one of the pixel array. One of the examples of these periodic structures is a touch screen electrode panel (TSP) mesh. Analytical method for visibility simulation using human eye’s Contrast Sensitivity Function (CSF) is developed. The method is based on the representation of the periodical structures as a 2D Fourier series and visibility criterion as a root mean square value of the moiré pattern. The resulting visibility dependence on TSP mesh parameters is described by the form of F/θ-plot. By optimizing the geometrical structure of TSP electrode, the lowest visibility on the metal mesh was realized for the transparent touch screen with the newly proposed design method.

Development of Targeted Stimulus and Synchronized Detection System for Graphene Photodetectors investigation at Nano-scale

Lianqing Liu, Gongxin Li, Yuechao Wang, and Wenxue Wang

Doc ID: 332983 Received 31 May 2018; Accepted 23 Aug 2018; Posted 27 Aug 2018  View: PDF

Abstract: Little is known about the impact of different locations of graphene upon photon absorption on photocurrent generation and how to precisely calibrate photoelectric properties of graphene photodetectors. We propose a system of targeted stimulus and synchronized detection for photoelectric properties of graphene photodetectors. Precision of targeted stimulus of the system can be adjusted at nano-scale using a spatial light modulator. The system is used to calibrate photoelectric properties of a graphene photodetector and investigate photocurrents generation upon photon absorption at different points of graphene. The system offers a general way to measure photoelectric properties of nanophotodetectors as well as biological cells at nano-scale.

Compact and Low-crosstalk Mode (de)Multiplexer Using Triple Plasmonic-dielectric Waveguides Based Directional Coupler

Weifeng Jiang, Fangyuan Cheng, Ji Xu, and hongdan wan

Doc ID: 334185 Received 01 Jun 2018; Accepted 23 Aug 2018; Posted 24 Aug 2018  View: PDF

Abstract: A compact and low-crosstalk mode (de)multiplexer [(De)MUX] is proposed based on a triple-waveguide coupler, consisting of a hybrid plasmonic waveguide (HPW) in between two outer silicon waveguides. The proposed quasi-TM0 and quasi-TM1 mode (De)MUX is optimized by using the full-vectorial finite element method and three-dimensional full-vectorial finite difference time domain method sequentially. The numerical results show that the proposed mode (De)MUX is with a compact coupling length of 7.5 μm, an ultra-low mode crosstalk of -30 dB, an insertion loss of 0.32 dB at 1550 nm and an extinction ratio of >15 dB over the full C-band. The fabrication tolerance of the proposed mode (De)MUX is also investigated in detail.

Propagation of electromagnetic waves through non-uniform dielectric layers

Michal Bednarik and Milan Cervenka

Doc ID: 331028 Received 07 May 2018; Accepted 22 Aug 2018; Posted 22 Aug 2018  View: PDF

Abstract: The propagation of TE and TM polarized electromagnetic waves through a dielectric layer with spatial variation of refractive index is reported in this article. The relative permittivity of the layer is assumed to be graded along the thickness direction, its spatial variation is described by a quartic polynomial. The corresponding model equations are the Helmholtz equations with variable coefficients that can be transformed to the triconfluent Heun equation a local exact solution of which is expressed in terms of the tricofluent Heun functions. The found solutions are comprehensive in the sense that they cover many particular cases due to a variability of four optional parameters (coefficients) of the quartic polynomial. The found general local solution for a TE-polarized electromagnetic wave was employed for the calculation of transmission properties of a periodic one-dimensional photonic crystal using the Floquet theory.

Large Nonlinear Refraction in Pulsed Laser Deposited BCZT Thin-Films on Quartz Substrates

Sri Sadhu Pavan Prashanth, Martando Rath, Saikiran Posam, sai Muthukumar, M.S.R. Rao, and Varma K.B.R

Doc ID: 335765 Received 21 Jun 2018; Accepted 20 Aug 2018; Posted 22 Aug 2018  View: PDF

Abstract: Optical thin-films based on ferroelectric materials are forerunners for novel optoelectronic and photonic applications. In this report, we present the nonlinear optical response of a novel ferroelectric phase of barium titanate which is highly desired alternative to lead based perovskites. Ferroelectric Ba₀.₈₅Ca₀.₁₅Zr₀.₁Ti₀.₉O₃ (BCZT) thin-films of different thicknesses were deposited on quartz substrates at 700 ⁰C using pulsed laser deposition technique. The crystallinity of the thin-films was evaluated via X-ray diffraction (XRD) and the surface morphology was probed by atomic force microscopy (AFM). BCZT thin-film was subjected to high resolution transmission electron microscopy (HRTEM) for validating crystallite size obtained by X-ray diffraction studies. The dispersion of refractive indices with varying the thickness of the films was calculated from experimentally obtained UV-Visible transmission spectra. The optical nonlinearity of these thin-films was measured by closed aperture Z-Scan technique with He-Ne laser as excitation source. The films exhibited high optical nonlinearity and the nonlinear refractive index was around 5 x10-7 m²/W. The enhanced nonlinear refraction in these thin-films at continuous-wave (CW) regime suggests that they have potential application in nonlinear photonic devices.

Laser amplification in Yb:YAG thin rods of different geometries: simulation and experiment

Byunghak Lee, Sergey Chizhov, Elena Sall, Ji Kim, Ivan Kuznetsov, Ivan Mukhin, Oleg Palashov, Guang-Hoon Kim, Vladimir Yashin, and Olga Vadimova

Doc ID: 338515 Received 12 Jul 2018; Accepted 20 Aug 2018; Posted 22 Aug 2018  View: PDF

Abstract: The numerical model for simulation of broadband amplification in a thin rod and thin tapered rod active elements was developed. The amplification of ultrashort laser pulses in three gain modules of different geometries was studied experimentally; the results of experiments were used for validation of the elaborated numerical model. The laser system consisting from an ultrafast solid-state master oscillator and a two-stage thin-rod amplifier has been constructed. With the use of the developed numerical model, the active elements parameters optimization was carried out in order to increase the output power of the elaborated laser system.

Optomechanical Entanglement of Remote Microwave Cavities

Brian Clader and Samuel Hedemann

Doc ID: 328425 Received 18 Apr 2018; Accepted 16 Aug 2018; Posted 17 Aug 2018  View: PDF

Abstract: We examine the entanglement properties of a system that represents two driven microwave cavities each optomechanically coupled to two separate driven optical cavities which are connected by a single-mode optical fiber. The results suggest that it may be possible to achieve near-maximal entanglement of the microwave cavities, thus allowing a teleportation scheme to enable interactions for hybrid quantum computing of superconducting qubits with optical interconnects.

Surface structuring of rutile TiO2 (100) and (001) single crystals with femtosecond pulsed laser irradiation

Luc Museur, Aleka Manousaki, Demetrios Anglos, Tsibidis Giorgos, and Andrei KANAEV

Doc ID: 336293 Received 27 Jun 2018; Accepted 13 Aug 2018; Posted 20 Aug 2018  View: PDF

Abstract: Laser-based surface patterning of rutile TiO2 monocrystals with (001) and (100) surface orientation is investigated following irradiation by femtosecond KrF laser (248 nm) with variable fluences and multiple linearly polarized beams. Different types of structures were observed: volcano-like craters, nanoparticle-covered structures, ripples and grooves. Furthermore, two kinds of distinct laser induced periodic structures, 1D and 2D patterns were observed Morphological maps of characteristic surface morphologies were produced for each crystalline orientation, which indicate the significant influence of the crystalline anisotropy.

Impact of ordering of gold nanohole arrays on refractive index sensing

Padmanabhan Viswanath and Brindhu Malani

Doc ID: 332617 Received 29 May 2018; Accepted 11 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Hexagonally ordered gold nanohole arrays of various hole size having fixed thickness are fabricated using colloidal lithography. The degree of ordering of gold nanohole arrays were obtained using pair correlation function and bond-orientation order parameter. Reflectance studies show both localized surface plasmon resonance and propagating surface plasmon polaritons. These optical responses are found to be dependent on the hole size variations and their ordering. The spectral resolution of each plasmonicresonance dip is evaluated by full height/full width at half-maximum. It improves with the long-range ordering and higher bond-orientational order parameter. Based on order quantification and optical response, the optimal sample is chosen for refractive index sensing yielding sensitivity of 470.49 nm/RIU and figure of merit of 14.42.

Efficiently Modeling the Noise Performance of Short-Pulse Lasers with a Computational Implementation of Dynamical Methods

Shaokang Wang, Curtis Menyuk, and Thomas Carruthers

Doc ID: 336190 Received 27 Jun 2018; Accepted 05 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Lowering the output noise of short pulse lasers has been a long-standing effort for decades. Modeling the noise performance plays a crucial role in isolating the noise sources and reducing them. Modeling to date has either used analytical or semi-analytical implementation of dynamical methods or Monte Carlo simulations. The former approach is too simplified to accurately assess the noise performance in real laser systems, while the latter approach is too computationally slow to optimize the performance as parameters vary over a wide range. Here, we describe a computational implementation of dynamical methods that allows us to determine the noise performance of a passively modelocked laser within minutes on a desktop computer and is faster than Monte Carlo methods by a factor on the order of 1000 . We applythis method to characterize a laser that is locked using a fast saturable absorber—for example, a fiber-based nonlinear polarization rotation device—and a laser that is locked using a slow saturable absorber—for example, a semiconductor saturable absorbing mirror.

High-efficiency quantum key distribution without key sifting

Qi Guo, Ping Liu, Shaobo Gao, and chunyan li

Doc ID: 332693 Received 29 May 2018; Accepted 26 Jul 2018; Posted 28 Aug 2018  View: PDF

Abstract: In traditional quantum key distribution (QKD) protocol, both communication parties need to reconciliate their encoding basis to realize sharing secret keys. However, the process of basis reconciliation decreases the generation efficiency of the secret key and classical information is needed to be transmitted for every raw key. Based on quantum interference, we propose a high-efficiency quantum key distribution protocol without basis reconciliation. The presented protocol can greatly improve the generating efficiency of secret keys, reaching 100\% in the ideal case, and no classical information is needed. We also analyze the security of the protocol in detail, which shows the protocol is robust against common attack strategies. Furthermore, the protocol can be implemented with current technologies and open promising possibilities for quantum cryptography.

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