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High-energy ultrashort stretched pulse all-fiber erbium-doped ring laser with an improved free-running generation stability

Dmitriy Dvoretskiy, Stanislav Sazonkin, ILYA O. OREKHOV, Igor Kudelin, Alexey Pnev, Valeriy Karassik, Alexandr Krylov, and Lev K. Denisov

Doc ID: 330558 Received 27 Apr 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We report on the stable stretched pulses generation with a duration ~ 180 fs at a central wavelength of 1560 nm with an 30 mW average output power at a repetition rate ~ 11.3 MHz (with a signal-to-noise ratio at a fundamental frequency ~ 59 dB) with an Allan deviation of the pulse repetition frequency ~ 5.75·10^-9 for 1 s interval and a relative intensity noise < -101 dBc / Hz (30 Hz-1000 kHz). This corresponds to the < 14.7 kW maximum peak power and < 2.6 nJ maximum available pulse energy obtained immediately from the highly-nonlinear all-fiber laser resonator.

Four-wave mixing in air by bichromatic spectrally broadened femtosecond laser pulses

Virgilijus Vaicaitis and Viktorija Tamuliene

Doc ID: 331214 Received 08 May 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: The broadband infrared (in the range of 2 mm) and visible radiations were generated in air by focused two colour (wavelengths of about 791 nm and 1.2-1.6 mm, respectively) femtosecond laser pulses. The spectral and angular properties of the radiation generated in both spectral ranges allowed us to interpret it as a result of the interplay between spectral broadening and cascaded four-wave mixing of the incident and frequency-shifted light fields. Results of the numerical modelling of the propagation equation includingthe nonlinear Kerr term agrees well with the experiment.

Modulation instability in 2D waveguide arrays withalternating sign of refraction index

Kuppusamy Porsezian, Shafeeque A K, and Andrei Maimistov

Doc ID: 332750 Received 29 May 2018; Accepted 11 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We consider the propagation of coupled forward and backward waves in two dimensional arrays of alternatingwaveguides with positive and negative refractive indices. The array has the cross section in theform of face-centered square lattice. The unit cell consists of three different waveguides with differentoptical properties. We obtain the condensate solutions for electromagnetic pulse propagation in such arrayof waveguides. The base equations describing this model have the solution that corresponds to thestatic and homogeneous intensity distribution on the waveguides. The stability of these solution in bothnormal and anomalous dispersion regimes are also investigated using the modulation instability analysis.

Shock Physics at the Nanoscale

David Moore

Doc ID: 332074 Received 18 May 2018; Accepted 10 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Shock waves can achieve extreme states of pressure and temperature, of particular interest because those conditions can result in non-equilibrium material dynamics that evolve on ultrafast timescales. Examples of such phenomena include shock-induced chemistry and phase transitions. Traditional plate impact methods lack the necessary time and space resolution needed to observe the onset of ultrafast nanoscale phenomena. Sub-picosecond time scale and nanometer spatial scale shock compression and diagnostics methods have been developed to surmount such difficulties. This paper reviews a number of nanoscale shock wave generation methods, as well as the diagnostics that are applicable at these restrictive time and spatial scales.

Photosensitive center in CdTe:Sn: Photorefractive, spectroscopic, and magnetooptical studies

Konstantin Shcherbin, Serguey Odoulov, Francois Ramaz, Dean Evans, and Bernard Briat

Doc ID: 332395 Received 24 May 2018; Accepted 10 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Photorefractive properties of tin-doped CdTe crystals are studied. The material demonstrates sensitivity for low-intensity recording. One-center model of the space-charge formation perfectly describes the experimental results. Tin impurity center is characterized using the data of optical absorption and lightinduced absorption spectroscopy, pseudo 3-D mapping of the photoabsorption, magnetic circular dichroism and optical detection of magnetic resonance. Spectroscopic studies confirm appropriateness of the one-center model for describing the space charge formation with tin as a main photorefractive center. Optical ionization (neutralization) energies are estimated for phototransitions from Sn+ (1.14 eV) and Sn0 (1.09 eV). Possible ways for improvement of the photorefractive performances are discussed.

Multiple PT symmetry and tunable scattering behaviors in a heterojunction cavity

Feng Gao, Jia-Rui Dong, Yimou Liu, Yan Zhang, and Jin-Hui Wu

Doc ID: 320750 Received 31 Jan 2018; Accepted 09 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We study a heterojunction cavity with one vacuum gap inserted between two dielectric slabs of conjugate complex refractive indices, i.e. of balanced gain and loss. This cavity is found to exhibit a multiple PT symmetry characterized by alternate symmetric and broken phases when examined in terms of both eigenvalues of the scattering matrix. Scattering behaviors including reflection and transmission, however, should be classified into three distinct types because a transition region may exist between the symmetric and broken phases. It is of particular interest that vanishing reflectance could occur for light waves input from both left and right sides, though of different wave vectors, in the symmetric phases. Moreover, it is viable to attain unidirectional invisibility for light waves only input from the left side and simultaneously realize coherent perfect absorption and lasing for a given wave vector in the transition regions. These unique scattering behaviors can be easily tuned to suit a wide range of wave vectors by adjusting the gap width.

Low-loss forward and backward surface plasmons in a semiconductor nanowire coated by helical graphene strips

Vladimir Tuz, Volodymyr Fesenko, and Vitalii Shcherbinin

Doc ID: 332193 Received 21 May 2018; Accepted 04 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: In the long-wavelength approximation, the effective conductivity tensor is introduced for graphene ribbons (strips) placed periodically at the interface between two media. The resulting conducting surface is considered as a coating for semiconductor nanowire. For the hybrid waves of such nanowire the dispersion equations are obtained in explicit form. Two types of surface plasmons are found to exist: (i) the modified surface plasmons, which originate from the ordinary surface plasmons of a graphene-coated semiconductor nanowire, and (ii) the spoof plasmons, which arise on the array of graphene ribbons and may possess forward-wave and backward-wave dispersion. It is revealed that the spoof surface plasmons are low-loss ones, and their frequencies, field-confinement and group velocities can be tuned widely by adjusting the coil angle and width of helical graphene strips.

A compact frequency-stabilized pump laser for wavelength conversion in long-distance quantum communication

Kohei Ikeda, Yusuke Hisai, Kazumichi Yoshii, Hideo Kosaka, Feng-Lei Hong, and Tomoyuki Horikiri

Doc ID: 326543 Received 21 Mar 2018; Accepted 04 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: We demonstrate a compact frequency-stabilized laser at 1064 nm using Doppler-free saturation absorption spectroscopy of molecular iodine. The achieved laser frequency stability and linewidth are 5.7  10-12 (corresponding to an absolute frequency of 1.6 kHz) and 400 kHz, respectively. The developed frequency-stabilized laser can be used as a pump laser for wavelength conversion from visible to telecom (or vice versa) to connect quantum memories utilizing nitrogen-vacancy centers in diamond at remote nodes in fiber-based quantum communication.

Controlling the Trajectories of Self-Written Waveguides in Photopolymer

Ra'ed Malallah, Haoyu Li, Inbarasan Muniraj, Derek Cassidy, Nebras Alattar, John Healy, and John Sheridan

Doc ID: 327832 Received 12 Apr 2018; Accepted 03 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: The diffraction of a light beam as it propagates through a medium can be effectively compensated by self-trapping. A laser beam propagating through a nonlinear medium can generate a waveguiding action, i.e. a higher refractive index, along the direction of the light propagation. Experiments involving light beams illuminating the front surface of a solid bulk photopolymer sample are reported. The self-bending of parallel beams, (input simultaneously but separated in space), during the resulting self-writing process are studied. It is shown that there is strong correlation between the initial beam input separation distance and the resulting waveguide trajectories taken during channel formation. Finite element-based simulations are performed that predict the self-writing waveguides formation process, e.g. beam focusing, trapping and the deviations of the waveguide trajectories caused by adjacent beams. The model is shown to be in good qualitative agreement with observed experimental results.

Theoretical modeling of photo-induced lens formation in a polymerizable matrix containing quantum dots

Svitlana Bielykh, Tigran Galstian, and Victor Reshetnyak

Doc ID: 331461 Received 11 May 2018; Accepted 03 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: We present a theoretical model describing the dynamic modulation of the refractive index of quantum dot (QD) containing photo polymerizable mixture under the spatially non-uniform illumination. The case of a laser beam with Gaussian spatial intensity distribution is used to model the process of non-uniform polymerization, followed by the processes of diffusion of monomers, polymers and QDs. This results in the creation of a lens-like refractive index transversal distribution. The contribution of QDs is taken into account by using the conservation of the sum of volume fractions of polymers, monomers and QDs. Dynamic variations of different parameters influencing the lens formation and the focal length of the lens are obtained. In particular, it is shown how the change of time of irradiation varies the profile of the refractive index and, hence, controls the focal length of the lens.

Optical Phase Control of Coherent Pulse Stacking via Modulated Impulse Response

Yawei Yang, Lawrence Doolittle, Almantas Galvanauskas, Qiang Du, gang huang, John Ruppe, Tong Zhou, Russell wilcox, and Wim Leemans

Doc ID: 331880 Received 24 May 2018; Accepted 02 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: To stabilize the combined pulse energy for coherent temporal pulse stacking using interferometer cavities, we have developed a direct cavity phase measurement method, based on analysis of response to modulated probe pulses. An experiment has demonstrated optical phase control within 50 mrad for four cavities, resulting in combination of 25 pulses with 1.5% RMS stability over 30 hours.

The effects of Mn doping on the structural, linear and nonlinear optical properties of ZnO nanoparticles

Fahimeh Abrinaei and Nasiben Molahasani

Doc ID: 332547 Received 24 May 2018; Accepted 01 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: In this study, we reported on the synthesis and characterization of ZnO and Mn-doped ZnO nanoparticles (NPs) with 2, 5 and 15% Mn/ZnO prepared using the hydrothermal method. The morphological and structural properties of the Mn-doped ZnO NPs were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), and Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction patterns indicate that all of the samples have hexagonal wurtzite structure. The average diameters of Mn-doped ZnO NPs with different Mn ratios were estimated about 20-38 nm from FESEM images. Linear absorption coefficient and optical band gap energy of ZnO and Mn: ZnO NPs were calculated using UV-VIS spectroscopy. A decrease in Eg was observed by an increase in Mn concentration. The nonlinear optical (NLO) measurements have been performed using a nanosecond Nd: YAG pulse laser by the Z-scan technique. Both pure and Mn-doped ZnO NPs exhibited a negative NLO index of refraction at 532 nm which is related to a self-defocusing phenomenon. The NLO absorption of ZnO and Mn: ZnO NPs is attributed to two-photon absorption (TPA) combined with free carrier absorption. Furthermore, the third-order nonlinear susceptibilities of pure and Mn-doped ZnO NPs were varied between 1.2- 2.5×10−9 esu, depending on Mn contents. The results suggest that ZnO and Mn: ZnO NPs synthesized by the hydrothermal method may be a promising candidate for the NLO applications at 532 nm as well as Mn dopant can improve the NLO properties of ZnO NPs.

Simulation of a multimode fiber interferometer using averaged characteristics approach

Oleg Kotov, Mikhail Bisyarin, Ivan Chapalo, and Alexander Petrov

Doc ID: 314998 Received 05 Dec 2017; Accepted 01 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: A new method of analytical representation and numerical simulation of multimode fiber interferometer signals is developed. A system of averaged normalized characteristics, called amplitude and spectral characteristics, is introduced for this end. Interferometer signals generated by fiber length variation or laser frequency modulation were investigated at various parameters of the fiber. Joint usage of amplitude and spectral characteristics proved to substantially broaden dynamical range of measurements of weak and strong external disturbances of the fiber. The method may be used for analysis and design of various optical sensor schemes with multimode fiber interferometers. It is also usable for estimating modal noise characteristics in optical systems with undesirable effects of intermodal interference.

Lasing of optically pumped large droplets: instant and gradual blue shift

Mihai Pascu, Mihai Boni, Ionut Andrei, and Angela Staicu

Doc ID: 326209 Received 16 Mar 2018; Accepted 29 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: Results about the interaction of 532 nm pulsed laser beam with individual pendant Rhodamine 6G dye droplets of large size parameter, x ≈ 7300, are reported. By varying dye concentration and pumping energy are obtained typical fluorescence bands detected in such cases and a narrow, instantly or gradually blue shifted band assigned to lasing effect at droplet surface. The maximum blue shift value of the lasing peak wavelength is associated with the maximum of dye fluorescence gain curve when self-absorption effects are not present. Lasing peak position is not further influenced by pumping energy or droplet diameter decrease after lasing reaches the wavelength of gain curve peak.

Goos-Hänchen shift for Gaussian beams impinging on monolayer MoS₂-coated surfaces

Akash Das and Manik Pradhan

Doc ID: 330562 Received 30 Apr 2018; Accepted 29 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We report a detailed theoretical study of the Goos-Hänchen (GH) shift for a fundamental Gaussian beam on the surface coated with monolayer molybdenum disulfide (MoS₂), a promising two-dimensional transition metal dichalcogenide (2D-TMDC) and a direct band-gap semiconductor. A general model has been developed to predict the GH shifts on monolayer MoS₂-coated surfaces for light beam with different wavelengths. In contrary to the conventional GH shift which is observed for total internal reflection only, here we predict finite spatial and angular GH shift for both partial (PR) and total internal reflection (TIR) conditions. Our analysis revealed that the observation of the giant negative spatial GH shift on MoS₂-coated surfaces is attributed to the surface conductivity of MoS₂ monolayer which has never been explored before. Furthermore, we find that the GH shifts are dependent on the mode of polarization, the wavelength of incident beam along with the nature of surfaces. This deepens our understanding of the unusual behaviour of GH shift near the Brewster’s angle as well as the critical angle of incidence. We expect that our findings will lead to several new applications of MoS₂ in sensors and device technology.

On sensitivity limitations of a dichromatic optical detection of a classical mechanical force

Andrey Matsko and Sergey Vyatchanin

Doc ID: 331647 Received 14 May 2018; Accepted 29 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: We apply the strategy of the back action evading measurement of a quadrature component of mechanical motion of a test mass to detection of a classical force acting on the mass (1) and study both classical and quantum limitations of the technique. We are considering a resonant displacement transducer interrogated with a dichromatic optical pump as a model system in this study. The transducer is represented by a Fabry Perot cavity with a totally reflecting movable end mirror the resonant force of interest acts upon. The cavity is pumped with two coherent optical carriers equally detuned from one of the cavity resonances. We show that the quantum back action cannot be completely excluded from the measurement result due to the dynamic instability of the opto-mechanical system that either limits the allowable power of the optical pump or calls for introducing an asymmetry to the pump configuration destroying the quantum nondemolition nature of the measurement.

Characterization of over-octave spanning laser pulses using interferometric imaging of self-diffraction

Christoph Leithold, Jan Reislöhner, Jesús Delgado Aguillón, and Adrian Pfeiffer

Doc ID: 330468 Received 26 Apr 2018; Accepted 27 Jun 2018; Posted 29 Jun 2018  View: PDF

Abstract: Interferometric, spectrally resolved imaging of self-diffraction is a recently introduced technique for the temporal and spatial characterization of laser pulses. Using either an analytical or an iterative method, pulse retrieval is achieved for two independent laser pulses in a non-collinear geometry. The method is not sensitive to beam alignment in the nonlinear medium and does not require two identical copies of one laser pulse. Here, it is explored how the method can be applied to over-octave spanning waveforms, using numerically generated data. Two configurations are presented. One configuration provides the simultaneous characterization of two pulses but is limited to a bandwidth of less than 1.6 octaves (a frequency ratio less than 1:3 between the lowest and the highest frequencies in the spectrum). The other configuration is suited for a bandwidth with a frequency ratio up to roughly 1:5, but it provides the characterization of only one out of two independent pulses.

Efficient and accurate synthesis of complex Bragg grating waveguide in dispersive silicon structures

Chenghao Feng, Richard Soref, Ray Chen, Xiaochuan Xu, and Wei Jiang

Doc ID: 330873 Received 03 May 2018; Accepted 27 Jun 2018; Posted 28 Jun 2018  View: PDF

Abstract: The complex Bragg-grating waveguide (CBGW) is a semiconductor strip channel with many side corrugations or teeth. The layer-peeling(LP) and layer-adding(LA) algorithms have shown that the CBGW can be designed to offer an arbitrary pre-selected spectral-transmission profile having multiple peaks, but such a structure generally requires a huge number of teeth and a long length scale. In this paper, we propose a modified LP/LA algorithm that can significantly reduce CBGW structure length and develop accompanying time/memory-saving simulation procedures. Dispersion engineering is also introduced to significantly improve the accuracy of the LP/LA algorithm for high-index-contrast structures. A CBGW for a transmission spectrum with three passbands is designed and optimized on the SOI platform. Results show that our design can shorten the length of the CBGW by 10 times compared to the original design by LP algorithm. Compared to the original LP/LA algorithm, the modified algorithm with dispersion engineering significantly improves the matching between the reconstructed transmission and the actual spectrum obtained by simulation.

Multiphoton Discrete Fractional Fourier Dynamics in Waveguide Beam Splitters

Konrad Tschernig, Roberto Leon Montiel, Omar Magana Loaiza, Alexander Szameit, Kurt Busch, and Armando Leija

Doc ID: 332035 Received 17 May 2018; Accepted 26 Jun 2018; Posted 28 Jun 2018  View: PDF

Abstract: We demonstrate that when a waveguide beam splitter (BS) is excited by N indistinguishable photons, the arising multiphoton states evolve in a way as if they were coupled to each other with coupling strengths that are identical to the ones exhibited by a discrete fractional Fourier system. Based on the properties of the fractional Fourier transform, we then derive a multiphoton suppression law for 50/50 BSs, thereby generalizing the Hong-Ou-Mandel effect. Furthermore, we examine the possibility of performing simulta- neous multiphoton quantum random walks by using a single waveguide BS in combination with photon number resolving detectors. We anticipate that the multiphoton lattice-like structures unveiled in this work will be useful to identify new effects and applications of high-dimensional multiphoton states.

Sublinearly-chirped metalenses for forming abruptly autofocusing cylindrically polarized beams

Sergey Degtyarev, Svetlana Khonina, and Sergey Volotovsky

Doc ID: 327731 Received 05 Apr 2018; Accepted 26 Jun 2018; Posted 28 Jun 2018  View: PDF

Abstract: We propose a metalens which forms an abruptly autofocusing cylindrically polarized laser beam. The main principle of the metalens is based on combining two elements: a subwavelength polarization grating and an autofocusing sublinearly-chirped lens. Subwavelength polarizing grating is calculated separately. It is shown that the grating can effectively convert linearly polarized initial beam into radially polarized beam. It is demonstrated that combining the polarization convertor and focusing phase lens, we both increase polarization conversion efficiency and decrease the quantity of optical elements in an arrangement. Wave propagation through the metalens is numerically simulated with the finite element method which is implemented in Comsol Multiphysics software. Polarization and phase conversion is calculated in the near-zone behind the metalens. Further wave propagation and focusing are simulated with Rayleath-Sommerfeld diffraction integrals. Metalenses for forming both diffraction-free and abruptly autofocusing radially-polarized beams are under investigation.

Quantum noise of parametric amplification in phase-sensitive/insensitive intermediate condition

Kyo Inoue

Doc ID: 325907 Received 16 Mar 2018; Accepted 25 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: Phase-sensitive amplification (PSA) is a particular type of optical parametric amplification (OPA), which features a low-noise property such that the quantum-limited noise figure is 0 dB. The PSA operation is typically achieved when the signal and idler spectra are degenerate in optical parametric interactions, i.e., the degenerate OPA condition. However, for a spectrally broadened incident light, these two spectra can be partially degenerate. The present work investigates the noise property of OPA in such conditions in terms of quantum mechanics. The results quantitatively indicate the intermediate properties between PSA and phase-insensitive amplification

An electro-optic controllable TE/TM polarization convertor based on the GaN/Al₀.₃Ga₀.₇N superlattice waveguide

Tao Wang and Guangming He

Doc ID: 331000 Received 07 May 2018; Accepted 20 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: An electro-optic controllable TE/TM polarization convertor based on the GaN/Al₀.₃Ga₀.₇N superlattice waveguide is proposed for actively controlling the output polarization state. We use the highly accurate and efficient full vector mode matching method to evaluate its performance. The result indicates that the output polarization state can be actively controlled in a full 0º~90º range by applying the adjustable voltage on this polarization convertor, and that a full TE↔TM conversion can also be realized by applying no voltage, with a conversion efficiency of 99.9% and an insertion loss of 0.03 dB. We further investigate the deviation effect of the etching width or the operating wavelength on TE↔TM conversion. In order to counteract deterioration on conversion efficiency brought in by the deviation, a simple compensation method is presented by actively adjusting the voltage to certain value.

Robust Increase of the Optical Forces in Waveguide Based Optical Tweezers Using V Groove Structure

Amir Habibzadeh-Sharif and Mahdi Sahafi

Doc ID: 326355 Received 26 Mar 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: Waveguide-based optical tweezers have significant advantages for particle trapping and transporting in optofluidic chips due to their simple fabrication process. However, for effective trapping of nanoparticles, a high power input field should be applied, which limits their applications. Here, we numerically show that a silicon on insulator (SOI) based V groove waveguide has a much higher capability to trap nanoparticles compared with the traditional waveguides. According to the calculations, the trapping force exerted by the V-groove waveguide to a 5 nm radius nanoparticle can be 14 times greater than that of the strip waveguide. The scattering force is 5 times larger in the same conditions. This structure would be very useful to be integrated into a lab on a chip system to form a particle delivery and analysis device.

Optical corral using a standing-wave Bessel beam

Keith Bonin and Chad McKell

Doc ID: 328104 Received 12 Apr 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: Here we create a series of optical corrals and calculate their potential energy profile. A standing wave Bessel beam is used to form traps in 1D (along the optical axis), and corrals in 2D, in planes perpendicular to the optical axis at the antinode regions of the standing waves. These optical corrals are formed by an axicon-generated Bessel beam that is retro-reflected back onto itself. We report on Mie calculations of the 2D optical corral and then compare the resulting probability distributions to those observed for latex particles of diameters 100, 200, and 300 nm. The experimental radial probability density function of tracked particles closely mimics the theoretical optical structure of a Bessel standing-wave corral. The Bessel standing-wave corrals we have characterized are being developed to measure rotational diffusion and torques on micro- and nanorods to help understand microfluidic behavior. The maximum forces on our small beads in the diffraction-free central zone of the Bessel beam standing wave are F_|| = 0.5 pN and F_perp = 0.1 pN.

A Lie algebraic approach to a nonstationary atom-cavity system

Jose Recamier, carlos gonzalez gutierrez, Octavio Sánchez, Ricardo Roman, and Manuel Berrondo

Doc ID: 328955 Received 20 Apr 2018; Accepted 19 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: In this work we study the generation of photons inside an ideal cavity with resonantly oscillating boundaries in the presence of a two-level atom. We make use of Lie algebraic techniques to obtain an approximate time-evolution operator and evaluate not only the resonant and dispersive regimes but also explore different regions of parameters. We have found a very good agreement between our approximate results and those obtained by numerical means.

Numerical Investigations on Polymer-Based Bent Couplers: Refractive Index Modulation, Offset Tolerance, Curvature, and Curing Time

Monali Suar, Maik Rahlves, Bernhard Roth, and Eduard Reithmeier

Doc ID: 326623 Received 21 Mar 2018; Accepted 15 Jun 2018; Posted 20 Jun 2018  View: PDF

Abstract: A diffusion-based material model is implemented and linked to the Crank Nicholson beam propagation method to carry out numerical investigations on self-written bent waveguide couplers on polymer basis. Such couplers are established in a photopolymer mixture when two opposing Gaussian laser beams with offset or gap along their propagation axes are traversed through the medium and the beams, eventually, get self-trapped. In this work, numerical investigations of the processes involved with respect to temporal dynamics of refractive index modulation and the corresponding intensity profiles are presented. We also show that compensation of misalignments or gaps is possible as the coupling length of the structure increases. Furthermore, we report and analyze the curing time and curvature of the bent couplers which are regulated by control of model parameters such as propagation distance between opposing beams, component concentrations, and the value of the rate constant during the simulation process.

A fully relativistic description of the power spectrum

Octavian Postavaru

Doc ID: 324775 Received 26 Feb 2018; Accepted 08 Jun 2018; Posted 06 Jul 2018  View: PDF

Abstract: Resonance fluorescence of laser-driven atoms is studied in the relativistic regime by solving the time-dependent Dirac equation in a multi-levelmodel. Electron spin and retardation of the electron-photon interaction gives rise to new phenomena such as splitting of sideband peaks andmodification of the Rabi oscillator frequencies not explainable in a non-relativistic theory. In our theoretical investigation, we show how applying coherent light with x-ray frequencies, the relativistic fluorescence spectrum can be exploited to determine atomic multipole matrix elements.

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