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Accepted papers to appear in an upcoming issue

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CW, Quasi-CW, Gain-Switched, and Femtosecond Burst-Mode Operation of Multi-Mode Diode-Pumped Cr:LiSAF Lasers

Umit Demirbas and Durmus Alp Emre ACAR

Doc ID: 269128 Received 23 Jun 2016; Accepted 26 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: In this study, we have investigated power scaling potential of diode-pumped Cr:LiSAF lasers upon pulsed pumping at varying pump pulsewidths (5 μs to 10 s) and duty cycles (2% to 100%). Compared to continuous-wave (cw) pumping, pulsed pumping allows the laser crystal to cool down while the pump is in off state, and enables better control of thermal effects and efficient laser operation in the pump active period. Depending on the parameters of the pulsed pump source, Cr:LiSAF laser operates in cw, quasi-cw, or gain switched regimes. In cw laser experiments, using a 20 mm long crystal with a relatively low Cr-doping of 0.8%, output powers as high as 2.4 W could be obtained at an absorbed pump power of 5.5 W. In quasi-cw operation, laser output powers as high as 3.1 W have been achieved, which represents a 30% improvement compared to cw case. In gain switched operation, pulses in the 1.35-5 µs range with peak powers up to 30 W have been observed at kHz repletion rates. Moreover, pulsed pumping has also been investigated in a cavity that is mode-locked with a saturable Bragg reflector, to investigate the advantage of femtosecond burst-mode operation compared to cw mode-locking. In femtosecond burst mode operation, 250-fs long pulses around 815 nm at a 106 MHz repletion rate with a burst average power of 1.1 W has been acquired. The corresponding pulse energy and peak power of the femtosecond pulses were 10.3 nJ and 36.6 kW, respectively. This represents a 2 fold improvement in pulse energies compared to cw mode-locking. The power levels obtained in this study was limited by the available pump power, and future studies in this direction has the potential to scale the output powers of the Cr:LiSAF laser above 10-W level.

Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism

Matthew Foreman, Florian Sedlmeir, Harald Schwefel, and Gerd Leuchs

Doc ID: 270908 Received 21 Jul 2016; Accepted 26 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: Optical whispering gallery mode (WGM) resonators are a powerful and versatile tool used in many branches of science. Fine tuning of the central frequency and line width of individual resonances is however desirable in a number of applications including frequency conversion, optical communications and efficient light-matter coupling. To this end we present a detailed theoretical analysis of dielectric tuning of WGMs supported in axisymmetric resonators. Using the Bethe-Schwinger equation and adopting an angular spectrum field representation we study the resonance shift and mode broadening of high Q WGMs when a planar dielectric substrate is brought close to the resonator. Particular focus is given to use of a uniaxial substrate with an arbitrarily aligned optic axis. Competing red and blue resonance shifts (~30 MHz), deriving from generation of a near field material polarisation and back action from the radiation continuum respectively, are found. Anomalous resonance shifts can hence be observed depending on the substrate material, whereas mode broadening on the order of ~50 MHz can also be simply realised. Furthermore, polarisation selective coupling with extinction ratios of > 10^4 can be achieved when the resonator and substrate are of the same composition and their optic axes are chosen correctly. Double refraction and properties of out-coupled beams are also discussed.

Femtosecond mid-IR difference-frequency generation in HgGa2S4 at 80 MHz

Valentin Petrov, Marcus Beutler, Ingo Rimke, Edlef Büttner, and Valeriy Badikov

Doc ID: 268233 Received 13 Jun 2016; Accepted 25 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: We employ HgGa2S4 for difference-frequency generation between signal and idler of a synchronously pumped femtosecond optical parametric oscillator at a repetition rate of 80 MHz achieving continuous tuning from ~4 µm (33 mW) to ~12 µm (>0.5 mW) and pulse durations ~220-fs.

Fabrication and characterization of step-index tellurite fibers with varying numerical aperture for near- and mid-infrared nonlinear optics

Clement Strutynski, Jérémy Picot-Clémente, Arnaud Lemiere, Paul froidevaux, frederic desevedavy, Gregory Gadret, Jules jean-charles, Bertrand Kibler, and Frederic Smektala

Doc ID: 269474 Received 30 Jun 2016; Accepted 25 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: We present an overview of the fabrication process and characterization of tellurite, germanate and germanate-tellurite step-index fibers with different index contrasts. Several compatible core/cladding glass pairs were first explored for fiber manufacturing under ambient atmosphere. The potential of the resulting waveguides for nonlinear optics is revealed by means of supercontinuum generation experiments using a near-infrared femtosecond fiber laser. Fabrication of the glass preforms was also adapted to dehydration procedures, allowing the drawing of low-OH step-index tellurite fibers. The beneficial impact of glass purification on supercontinuum generation towards the mid-infrared region is confirmed.

Localized plasmons induced by spatial conductivity modulation in graphene

Chris Beckerleg and Euan Hendry

Doc ID: 269445 Received 28 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: The effect of inducing a one dimensional periodic modulation in the conductivity of both a single and double layer of graphene is investigated using analytical modelling. By employing a modal matching approach, we find deep transmission minima associated with hybridised resonances of the modes supported by low and high conductivity regions. By carefully tuning the conductivity profile, we show that that a resonant absorption approaching 50\% can be achieved when both regions are made dipole resonant. Such plasmonic cavities may be a promising route to eliminating plasmonic losses typically introduced when etching graphene.

General solution to nonlinear optical quantum graphs using Dalgarno-Lewis summation techniques

Richard Lytel, Mark Kuzyk, and Sean Mossman

Doc ID: 272164 Received 21 Jul 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We develop an algorithm to apply the Dalgarno-Lewis (DL) perturbation theory to quantum graphs with multiple, connected edges. We use it to calculate the nonlinear optical hyperpolarizability tensors for graphs and show that it replicates the sum over states computations, but executes ten to fifty times faster. DL requires only knowledge of the ground state of the graph, eliminating the requirement to determine all possible degeneracies of a complex network. The algorithm is general and may be applied to any quantum graph.

Stimulated Raman and Brillouin Scattering, Nonlinear Focusing, Thermal Blooming and Optical Breakdown of a Laser Beam Propagating in Water

Bahman Hafizi, John Palastro, Joseph Penano, Ted Jones, Luke Johnson, Michael Helle, Dmitri Kaganovich, Yu-hsin Chen, and alexander stamm

Doc ID: 267267 Received 02 Jun 2016; Accepted 22 Aug 2016; Posted 24 Aug 2016  View: PDF

Abstract: The physical processes associated with propagation of a high-power laser beam in a dielectric include self-focusing, stimulated Raman scattering, stimulated Brillouin scattering, thermal blooming, multiphoton and collisional ionization, and plasma formation. The interplay between these processes is analyzed using a reduced model consisting of a few differential equations that can be readily solved, enabling rapid variation of parameters and development of theoretical results for new experiments. Consistent with experimental results in the literature it is found that self-focusing has a dramatic effect on propagation of high-power laser beams in water. A significant portion of the pump laser energy is transferred to Stokes Raman forward scatter along with a smaller portion to Brillouin backscatter.

Applying universal scaling laws to identify the best molecular design paradigms for third-order nonlinear optics

Javier Perez-Moreno, Shoresh Shafei, and Mark Kuzyk

Doc ID: 264279 Received 29 Apr 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: The scaling of the fundamental limits of the second hyperpolarizability is used to define the intrinsic second hyperpolarizability, which aids in identifying material classes with ultralarge nonlinear-optical response per unit of molecular size. The intrinsic nonlinear response is a size-independent metric that we apply to comparing classes of molecular homologues, which are made by adding repeat units to extend their lengths. Several new figures of merit are proposed that quantify not only the intrinsic nonlinear response, but also how the second hyperpolarizability increases with size within a molecular class. Scaling types can be classified into sub-scaling, nominal scaling that follows the theory of limits, and super-scaling behavior. Super-scaling homologues that have large intrinsic nonlinearity are the most promising because they efficiently take advantage of increased size. We apply our approach to data in the literature to identify the best super-scaling molecular paradigms and articulate the important underlying parameters.

Understanding search behavior via search landscape analysis in design optimization of optical structures

Sacha Verweij and Shanhui Fan

Doc ID: 264384 Received 02 May 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Search algorithms play a crucial role in systematic design optimization of optical structures. We demonstrate how search landscape analysis sheds light on the behavior of search algorithms in this context and thereby leads to valuable insight. Specifically, we present a case study in which search landscape analysis demystifies the surprisingly-good performance of a simple stochastic local search algorithm --- restarted iterative best improvement --- on a challenging design optimization problem --- combinatorial design optimization of a multi-spatial-mode photonic crystal waveguide bend that preserves modal content. Moreover, the search landscape analysis leads to insight potentially valuable in design optimization of a broad class of optical structures.

Broadened optical spectrum of repetition-rate-multiplied erbium-doped fiber comb

Taro Hasegawa

Doc ID: 266772 Received 24 May 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Repetition rate of an erbium-doped fiber comb is multiplied by an optical cavity for filtering, and the optical spectral distribution is broadened in a highly nonlinear fiber. For erbium-doped fiber combs, filtering cavities are commonly used to obtain the high-repetition-rate combs by the repetition rate multiplication. After the multiplication, optical spectral broadening by a highly nonlinear fiber is necessary for applications to optical frequency measurements in broad bandwidth and astronomy. In this study, the broadened spectrum covers over the range from 1050 nm to 2250 nm, which is over an octave so that the determination of the filtered mode numbers is feasible. The optical power of the broadened beam within a narrow optical bandwidth is also measured in time domain and in frequency domain to examine the broadening property.

Simple and distortion-free optical sampling of terahertz pulses via heterodyne detection schemes

Jérôme Degert, Emmanuel Abraham, Eric FREYSZ, and Marion Cornet

Doc ID: 269368 Received 27 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We present and demonstrate experimentally two simple and distortion free methods to sample terahertz pulse in zinc blende-type crystals like ZnTe or GaP. They are based on an optical heterodyne detection scheme which makes it possible to measure the terahertz field by detecting the optical probe beam or its second harmonic. Both are compared to conventional electro-optic sampling and give results in good agreement with the later.

Application of Range Migration Algorithms to Imaging with a Dynamic Metasurface Antenna

Laura Maria Pulido Mancera, Thomas Fromenteze, Timothy Sleasman, Michael Boyarsky, Mohammadreza F. Imani, Matt Reynolds, and David Smith

Doc ID: 268569 Received 24 Jun 2016; Accepted 21 Aug 2016; Posted 24 Aug 2016  View: PDF

Abstract: Dynamic metasurface antennas are planar structures that exhibit remarkable capabilities in controlling electromagnetic wave-fronts, advantages which are particularly attractive for microwave imaging. These antennas exhibit strong frequency dispersion and produce rapidly varying radiation patterns. Such behavior presents unique challenges for integration with conventional imaging algorithms. We adapt the range migration algorithm (RMA) for use with dynamic metasurfaces and propose a preprocessing step that ultimately allows for expression of the measurements in the spatial frequency domain, from which the fast Fourier transform can efficiently reconstruct the scene. Numerical studies illustrate imaging performance using both conventional methods and the adapted RMA, demonstrating that the RMA can reconstruct images with comparable quality in a fraction of the time. The algorithm can be extended to a broad class of complex antennas for application in synthetic aperture radar and MIMO imaging.

The static hyperpolarizability of space-fractional quantum systems

Nathan Dawson

Doc ID: 270092 Received 07 Jul 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: The nonlinear response is investigated for a space-fractional quantum mechanical system subject to a static electric field. Expressions for the polarizability and hyperpolarizability are derived from the fractional Schr\"{o}dinger equation in the particle-centric view under the three-level ansatz. Two types of asymmetric single-particle quantum systems are studied and both the linear and first nonlinear response to the perturbing field are analyzed with respect to the space-fractional parameter.

Applying universal scaling laws to identify the best molecular design paradigms for second-order nonlinear optics

Javier Perez-Moreno, Shoresh Shafei, and Mark Kuzyk

Doc ID: 264273 Received 29 Apr 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We apply scaling and the theory of the fundamental limits of the second-order molecular susceptibility to identify material classes with ultralarge nonlinear-optical response. Size effects are removed by normalizing all nonlinearities to get intrinsic values so that the scaling behavior of a series of molecular homologues can be determined. Several new figures of merit are proposed that quantify the desirable properties for molecules that can be designed by adding a sequence of repeat units, and used in the assessment of the data. Three molecular classes are found. They are characterized by sub-scaling, nominal scaling, or super-scaling. Super-scaling homologues most efficiently take advantage of increased size. We apply our approach to data currently available in the literature to identify the best super-scaling molecular paradigms with the aim of identifying desirable traits of new materials.

Generation and characterization of 2.2 W-level 318.6 nm narrow-linewidth ultra-violet laser

Junmin Wang, Jieying Wang, Jiandong Bai, and Jun He

Doc ID: 268256 Received 13 Jun 2016; Accepted 18 Aug 2016; Posted 18 Aug 2016  View: PDF

Abstract: We have demonstrated a high-power and narrow-linewidth ultra-violet (UV) laser system at 318.6 nm for single-step 6S1/2-nP (n=70~100) Rydberg excitation of cesium atoms. Based on commercial fiber lasers and efficient nonlinear frequency conversion technology, our system can generate 2.26 W UV laser output from cavity-enhanced second-harmonic generation (SHG) followed by sum-frequency generation (SFG) of two infrared lasers at 1560.5 nm and 1076.9 nm. The maximum doubling efficiency is 57.3%. The enhanced doubling cavity is actively stabilized by using the PDH modulation method, while the 637.2 nm laser is indirectly modulated through the SFG process which transfers modulation from the 1560.5 nm seed laser to the red laser. The typical UV laser power fluctuation is less than 0.87% over 30 minutes, and the continuously tunable range of the UV laser frequency is more than 6 GHz.

Semiconducting Subwavelength and Non-Subwavelength Grating Micro Ring Resonator as A Femtosecond Time Delayer-A Comparative Analysis

Iraj S Amiri, M Ghasemi, mm ariannejad, and Harith Ahmad

Doc ID: 265442 Received 18 May 2016; Accepted 18 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We investigate the role of one subwavelength-size grating of silver as a reflector at different angular position of InAs based SWG and non-SWG micro ring resonators for the application of femtosecond time delayer. The usage of one silver grate as a reflector basically imposes high loss to the generated peaks of transmitting power in each port of the micro rings, but regardless the amount of the loss, the response of each micro ring is compared, respectively. The achieved results explicitly indicated the different delay lengths between measured peaks at the ports of micro rings as a function of the angular position of one silver grate. Furthermore, the dominant property of the SWG micro ring to govern the delay length is evident from the observed results.

Fast generation of three-dimensional entanglement between two spatially separated atoms via invariant-based shortcut

Xin Ji, Jin-Lei Wu, Chong Song, and Shou Zhang

Doc ID: 266925 Received 24 May 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: A scheme is proposed for the fast generation of three-dimensional entanglement between two atoms trapped in two cavities connected by a fiber via invariant-based shortcut to adiabatic passage. With the help of quantum Zeno dynamics, the technique of invariant-based shortcut is applied for the generation of two-atom three-dimensional entanglement. The numerical simulation results show that the target state can be generated in a short time with a high fidelity and the scheme is robust against the decoherence caused by the atomic spontaneous emission, photon leakage, and the variations in the parameters. Moreover, the scheme may be possible to be implemented with the current experimental technology.

Pancharatnam phase in non-separable states of light

Chithrabhanu Perumangatt, Gangireddy Salla, NIJIL LAL C.K., Ali Anwar, Aadhi A, and Ravindra Singh

Doc ID: 268869 Received 23 Jun 2016; Accepted 16 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: We generate the non-separable state of polarization and orbital angular momentum (OAM) using a laser beam. The generated state undergoes a cyclic polarization evolution which introduces a Pancharatnam geometric phase to the polarization state and in turn a relative phase in the non-separable state. We experimentally study the violation of Bell - CHSH inequality for different Pancharatnam phases introduced by various cyclic polarization evolutions with linear and circular states as measurement bases. While measuring in linear bases, the Bell-CHSH parameter oscillates with Pancharatnam phase. One can overcome this dependence by introducing a relative phase in one of the projecting state. However for measurement in circular bases, the Pancharatnam phase does not affect the Bell-CHSH violation.

Nonlinear tunnelling and robust energy transfer in sum frequency generation

Y. G. Xu, Jing Zhang, Haifei Zhu, Jie Zhang, Pingping Ma, Jiang Wang, Huanhuan Liu, and Yongfang Li

Doc ID: 265298 Received 18 May 2016; Accepted 14 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Based on the counter-diabatic protocol in quantum physics and the quasi-phase-matching method in nonlinear optics, we present a method of achieving robust energy transfer between sum frequency and signal fields in an optical crystal system by adding a counter-diabatic field (CDF). Adding the CDF does not loosen the adiabatic condition, but rather separates the single original diabatic step into two so that the system remains adiabatic. The resulting two diabatic steps exhibit nonlinear tunneling, where the second step is the inverse of the first one. The optimal adiabatic transition path was also analyzed in terms of Bloch vectors. Moreover, we predict the fabrication of the nonlinear optical crystal with the quasi-periodicity in terms of the CDF. Not only does this work provide a solid theoretical foundation for the design of nonlinear optical devices, but it also elucidates physical processes that can be applied in many areas of modern science ranging from quantum information processing and coherent manipulation of quantum systems to high-precision measurements.

Compression of Tunable Broadband Mid-IR Pulses with a Deformable Mirror Pulse Shaper

Munira Khalil, Trevor Courtney, Madhumitha Balasubramanian, and James Gaynor

Doc ID: 267974 Received 23 Jun 2016; Accepted 08 Aug 2016; Posted 18 Aug 2016  View: PDF

Abstract: To improve the utility of ultrafast infrared spectroscopy experiments, we have developed and actively compressed a tunable broadband mid-infrared (BBIR) source. The octave-spanning BBIR source is generated by a filamentation process of 800 nm and 400 nm pulses in a pressurized gas cell. To correct the higher-order dispersion effects in BBIR pulses, we have introduced a deformable mirror grating compressor, which uses an iterative genetic algorithm with optical feedback. Compression yields nearly transform limited BBIR pulses of 21 fs, or ~1.4 optical cycles at the center frequency, as measured by cross-correlation frequency resolved optical gating (XFROG).

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