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Femtosecond supercontinuum generation in scattering media

Aditya Dharmadhikari, Hema Ramachandran, and Jayashree Dharmadhikari

Doc ID: 346075 Received 17 Sep 2018; Accepted 12 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We report our results on the effect of random multiple scattering on the supercontinuum (SC) generation. Spectral measurements are performed on the SC generated when femtosecond laser pulses propagate in water containing randomly suspended microspheres. We observed that the SC emission in the presence of scatterers is significantly suppressed on the blue side of the spectrum as compared to that observed in neat water. We attribute this to the strong scattering of the shorter wavelengths that serves to stretch the pulse temporally. This reasoning is supported by our experiments in neat water where we alter the shape of the incident femtosecond pulse by means of an acousto-optic programmable dispersive filter (AOPDF), and find similar suppression on the blue side with the lengthening of the input pulse. We believe our study will help in understanding the physics governing the applications that involve transmission of high intensity ultrashort pulses through long distances in scattering media like the atmosphere and sea water.

A Reconfigurable Multi-Party Quantum Network Enabled by a Broadband Entangled Source

Eric Zhu, Costantino Corbari, Alexey Gladyshev, Peter Kazansky, Hoi-Kwong Lo, and Li Qian

Doc ID: 347221 Received 02 Oct 2018; Accepted 12 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We present a proof-of-principle experimental demonstration of a reconfigurable, multi-party quantum key distribution (QKD) scheme utilizing a poled fiber-based source of broadband polarization-entangled photon pairs and dense wavelength-division multiplexing (DWDM). The large bandwidth (> 90 nm centered about 1555 nm) and highly spectrally-correlated nature of the entangled source can be exploited to allow for the generation of more than 25 frequency-conjugate entangled pairs when aligned to the standard 200-GHz ITU grid. In this work, 3 frequency-conjugate entangled pairs are used to demonstrate QKD, with wavelength-selective switching done manually. The entangled pairs are delivered over 40 km of actual fiber, and an estimated secure key rate of up to 20 bits/s per bi-party is observed.

Searching for Evidence of Optical Rectification: Optically-Induced Nonlinear Photovoltage in a Capacitor Configuration

Somayeh M.A.Mirzaee and Jean-Michel Nunzi

Doc ID: 336296 Received 27 Jun 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: A current challenge in photonics is to design new versatile photodetectors based on optical rectification induced photo-voltage; these ones are more attractive than classical photodetectors because they do not really on band to band transitions. Identification of the origin of the photovoltage detected under intense illumination can sometimes be confusing due to the competition between several nonlinear processes. Examples of such processes are optical rectification, multiphoton absorption, and photothermal heating, all of which may result in the detection of a DC photovoltage in a capacitor configuration. Herein, differences between the resulting photovoltage from these processes are analyzed, and techniques are proposed to distinguish between optical rectification-induced DC-photovoltage and the photovoltage resulting from alternative effects.

Z-scan for non-Gaussian beams applied to phosphate glasses doped with Er$^{3+}-$Yb$^{3+}$ and Ag nanoparticles

Carlos Wiechers Medina, Alejandrina Martinez-Gamez, Miguel Vallejo-Hernández, Mauricio Rodríguez González, Xochitl Sanchez-Lozano, José Luis Lucio, and Lorena Velazquez-Ibarra

Doc ID: 338798 Received 17 Jul 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We report on the use of Z-scan with non Gaussian beams to probe the non linear optical properties of phosphate glasses doped with Er-Yr and silver nanoparticles. Experiments are performed by implemen\-ting the open aperture Z-scan technique with bimodal laser pumping ($LG_{00}$ and $LG_{20}$) at 908.6 nm. The analysis is performed using a simplified model that incorporates non linear absorption and saturation intensity of the samples, as well as energy transfer between the modes.The later is introduced since the optical active media act as intermediary.

Hollow-core fiber compression of a commercial Yb:KGW laser amplifier

John Beetar, Federico Rivas, Shima Gholam Mirzaeimoghadar, Yangyang Liu, and Michael Chini

Doc ID: 346002 Received 17 Sep 2018; Accepted 08 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: High-repetition rate high harmonic sources are desired for novel attosecond and time-resolved spectroscopies. One route to generating these sources is the nonlinear compression of high-average power Yb fiber and solid-state amplifiers, which can achieve >100 fs pulse duration with μJ to mJ pulse energy. Here, we demonstrate compression of 280 fs, 400 μJ pulses from a moderately high power (20 W) Yb:KGW laser amplifier to 15 fs. Few-cycle pulses (<5 cycles) with an energy of up to 200 μJ are obtained with a relatively simple scheme utilizing a xenon-filled hollow-core fiber and chirped mirror compressor and are used to generate XUV harmonics.

Light Bullet Supercontinuum

Sergey Chekalin, Alexander Dormidonov, Valery Kandidov, Viktor Kompanets, and Elizaveta Zaloznaya

Doc ID: 345936 Received 14 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: Some new results of experimental and numerical investigations on light bullets spectra are depicted. The scenario of supercontinuum and light field evolution from odd harmonics generation to the appearance of broadband spectrum and pulse compression up to single-cycle light bullet accompanied by onset of isolated anti-Stokes wing in spectra and high-frequency modulation of the light field is shown. The extension of dispersion equation for anti-Stokes band spectral maximum to all known experimental results obtained up to now for LBs spectra in different transparent dielectrics is presented. Decisive role of multiphoton ionization in short-wavelength cut-off of supercontinuum is revealed experimentally, numerically and analytically.

Terahertz vortex beam generation by infrared vector beam rectification

Ali Al Dhaybi, Jérôme Degert, Etienne Brasselet, Emmanuel Abraham, and Eric FREYSZ

Doc ID: 346696 Received 24 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We report on the conversion of an infrared vector beam into terahertz vortex beams using a <110>-cut ZnTe cubic crystal. First, we provide a theoretical analysis demonstrating how an infrared vector beam with the azimuthal order l can be transformed into a terahertz beam endowed with an orbital angular moment content that consists of optical vortices with topological charge ±2l. Experimentally, quasi-monochromatic terahertz vortex beams with topological charges +2 and -2 are produced and characterized both in amplitude and phase using real-time two-dimensional imaging of the terahertz electric field. These results enrich the terahertz vortex beam toolbox via the transfer of topological information from infrared to terahertzdomains.

A model for confined Tamm plasmon devices

Michael Adams, Benjamin Cemlyn, Ian Henning, Matthew Parker, Edmund Harbord, and Ruth Oulton

Doc ID: 344858 Received 03 Sep 2018; Accepted 08 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: It is shown that cavities formed between a multilayer quarter-wave Bragg reflector and a metal mirror which support Tamm plasmons can be modelled by using a hard-mirror approximation including appropriate penetration depths into the mirrors. Results from this model are in excellent agreement with those found by numerical methods. In addition Tamm modes that are laterally confined by the presence of a metallic disc deposited on the Bragg reflector can be described by the effective index model that is commonly used for vertical-cavity surface-emitting lasers (VCSELs). This enables the lateral modes confined by a circular disc to be found from conventional weakly-guiding waveguide theory similar to that used for optical fibres. The resonant wavelengths of these linearly-polarised (LP) guided modes are calculated as functions of disc diameter and other parameters.

A triple band cross-polarization converter based on ultra-thin graphene-integrated metasurface

yueke wang, zhifei yao, mengjia lu, and Chunyang Zhang

Doc ID: 345009 Received 05 Sep 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: We propose a triple band tunable and high-efficient reflected cross-polarization converter in the mid-infrared. The converter is composed of a metal ground plane, a dielectric layer, and double L-shaped graphene patch arrays. Triple bands(36.15, 48.95 and 52.20 THz) of cross-polarization conversion is achieved due to the superimposition of the two reflected components with a near 180(degree) phase difference. The tunable performance of our proposed can be realized by changing the Fermi energy and electron scattering time. Our idea is verified by the Finite Element Method simulation and paves a way to design multi-band of polarization converter.

New transfer-matrix method for frequency conversion in nonlinear multilayered structures based on coupled-amplitude equations

Jinjer Huang, Qian Feng, Xinlu Zhang, and Liuyang Zhang

Doc ID: 335699 Received 20 Jun 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: Based on complete coupled-amplitude equations, a new transfer-matrix method for non-collinear frequency conversion in nonlinear multilayered structures is proposed in consideration of oblique incidence and optical anisotropy. An analytic result is derived and is well interpreted by the bidirectional conversion processes. Its numerical model is developed into the transfer-matrix shooting method, suitable for the depleted pump case, and is verified by the shooting method upon coupled-wave equations through a second harmonic generation process in a hypothetical nonlinear structure. Analysis of the computation time in the numerical model demonstrates the efficiency is greatly improved compared with the classical shooting method.

Soret reverse saturable absorption of graphene oxide and its application in random lasers

Neda Ghofraniha, Radivoje Prizia, and Claudio Conti

Doc ID: 341095 Received 30 Jul 2018; Accepted 06 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: Carbon based materials have shown in past both saturable and reverse saturable absorption and among them in the last years the optical limiting behavior of graphene and graphene oxide caused by nonlinear scattering or fast nonlinear absorption effects have been consolidated. Here we demonstrate the thermal diffusion of graphene oxide flakes in dispersion asa new nonlinear effect not yet explored. We show a damping of 50% in the transmission and we follow its dynamics in time. Moreover, this nonlinearity, known as Soret effect, isused to limit the emission from a disordered random laser reaching a decrease of about 90% of the emitted peak intensity without a substantial alteration of the cavity efficiency.

Off-axis Terahertz parametric oscillator


Doc ID: 335565 Received 13 Aug 2018; Accepted 06 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We study an off-axis THz parametric oscillator and shown its superior performance over a conventional THz parametric generator. Furthermore, by pumping an off-axis lithium-niobate oscillator with a pulsed Nd:YAG laser having an axial-mode spacing matched to the THz oscillator’s mode spacing, we generated an ultra-broad red-shifted frequency comb between 1065 and 1085 nm at the output, which corresponds to a 4-octave-spanning THz-frequency comb in the idler spectrum. We also demonstrated a signal-seeded off-axis THz parametric oscillator, which generates 8-nJ narrow-line radiation at 2.1 THz and achieved 46% pump depletion in a 6.5 cm long crystal with only 4-mJ pump energy in a 460-ps pump pulse width. Furthermore, tuning between 3.6 and 4.9 THz for the generated radiation is also demonstrated in this work.

The effect of plasmonic mode on plasmon based lasers

Montacer Dridi, Colas Florent, and Chantal Compère

Doc ID: 344749 Received 03 Sep 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: For the last few years, plasmon based lasers have been investigated theoretically and experimentally. Several configurations have been reported. They are composed of quantum emitters coupled to a plasmonic structure. In this paper, we investigate the effect of the plasmon mode on the far-field and near-field characteristics of a nanolaser composed by a periodic array of metallic nanoparticles covered by gain materials under optical pumping. Two configurations were investigated. The first structure supported a localized surface plasmon (LSP) mode while the second a surface lattice plasmon (SLP) mode. This theoretical work relies on a semi-quantum calculations based on a four-level gain molecule and a time-domain approach. We demonstrated that lasing in a SLP mode nanolaser requires a lower concentration of quantum emitters and generates a higher far field emission with a lower threshold than lasing in LSP mode laser. At nanoscale, near-field enhancement at the emission wavelength and above the threshold is two orders of magnitude higher with the SLP than the LSP mode. Our results with a general character show that designing a plasmon based laser that sustains SLP mode will result in a better lasing efficiency than with a LSP mode.

Focusability of laser pulses at petawatt transport intensities in thin film compression

Deano Farinella, Jonathan Wheeler, Amina Hussein, John Nees, Matthew Stanfield, Nicholas Beier, Yong Ma, Gabriel Cojocaru, Razvan Ungureanu, Moana Pittman, Julien Demailly, Baynard Elsa, Riccardo Fabbri, Masruri Masruri, Radu Secareanu, Andrei Naziru, Razvan Dabu, Anatoly Maksimchuk, Karl Krushelnick, David Ros, Gérard Mourou, Toshiki Tajima, and Franklin Dollar

Doc ID: 346015 Received 18 Sep 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Thin film compression (TFC) and the focusability of high power laser pulses after self-phase modulation in thin films at transport intensities ( ~1 TW/cm²) for petawatt laser systems is demonstrated. High energy (~ 296 mJ) laser pulses are compressed from ~ 55 fs to ~ 31 fs. Additionally, the focusability of high power (~ 40-50 TW) flat-top laser pulses after spectral broadening in thin films is found to be largely maintained, showing only modest decreases in the energy contained in the central part of the focal spot. In light of these findings, TFC offers a method for moving toward single-cycle pulse durations at significantly higher energies than those found at present, and if beam instabilities can be mitigated maybe even higher intensities.

Phase controlled stable solitons in nonlinear fibers

Tarak Dey, Rajitha K V, Prasanta Panigrahi, and challenger mishra

Doc ID: 291167 Received 06 Aug 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Bright and grey coupled solitons, with complex envelope, are obtained as exact solutions of the system describing doped optical nonlinear fibers. The solitons formed are found to be free of amplitude and phase instabilities during its evolution, leading to the realization of stable soliton propagation. The phase of the input solitons play a crucial role in the formation of tanh-sech paired pulses. This soliton is not supported in a two level atomic medium and is exclusive to the Λ system.

Using graphene metasurface as a time-lens for ultrafast signal processing in the terahertz regime

Farshid Shatery, Hossein Babashah, and Zahra Kavehvash

Doc ID: 332867 Received 31 May 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Ultrafast signal processing in time-domain with high resolution and reconfigurability is a challenging task. This paper, for the first time, introduces a time-varying metasurface consisting of graphene micro-ribbon array for implementing time-lens in the terahertz domain. Given that the surface conductivity of graphene is proportional to the Fermi energy level in the THz regime, it is possible to change the phase property of the incident electromagnetic pulse by changing the Fermi level while the Fermi level itself is a function of voltage. Upon this fact, a quadratic temporal phase modulator, namely time-lens has been realized. This phase modulation is applied to the impinging signal in the time domain. The terahertz time-lens is a key element for processing of ultrafast temporal pulses. Using this time-lens a temporal filter in terahertz regime is implemented that has immense applications in the terahertz communication and spectroscopy.

Nanostructure for near total light absorption in a monolayer of graphene in the visible

Amirreza Mahigir and Georgios Veronis

Doc ID: 344261 Received 27 Aug 2018; Accepted 04 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: We propose a highly compact structure for near total light absorption in a monolayer of graphene in the visible. The structure consists of a grating slab covered with the graphene monolayer. The grating slab is separated from a metallic back reflector by a dielectric spacer. The structure supports a guided resonance in the visible. We show that such a structure enhances light-matter interactions in graphene via critical coupling by matching the external leakage rate of the guided resonance and the intrinsic loss rate in the system. We also show that, by using the dielectric spacer between the grating and the metallic mirror, near total absorption in the graphene monolayer can be achieved in the visible without the need for thick multilayer dielectric mirrors. The proposed structure could find applications in the design of efficient nanoscale visible-light photodetectors and modulators.

A novel semiconductor metamaterial design and its thermo-optical applications

afsaneh keshavarz and Zohreh Vafapour

Doc ID: 342444 Received 15 Aug 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: In this paper, a novel semiconductor metamaterial design based on electronically induced reflection (EIR) is proposed and its thermo-optic applications at the infrared frequency are investigated. The analytical results show that the peak resonance wavelength position depended very sensitively on the temperature of the structure. The room-temperature operation up to 9 um/K at T=295 K is achieved which is more than the other values in the literature. It is also shown that by increasing the temperature, the emission decreases which is promising for thermal regulation thermal tagging, and labeling applications. Furthermore, we demonstrate numerically that the thermal modulating application can be realized in the proposed semiconductor metamaterial. We achieved 15.4% of the modulation depth and 5.14% for the amplitude modulation depth which is great values. In general, the work has numerically proved that the thermo-optical design used has very good prospects for various negative differential thermos-optic emission technologies. Furthermore, this semiconductor-based metamaterial structure can develop the path in narrow-band thermo-optic modulating and sensing applications, and the like in the future.

Hybrid mode-locking of an all-fiber holmium laser

Serafima Filatova, Vladimir Kamynin, Natalia Arutyunyan, Anatoly Pozharov, Anton Trikshev, Irina Zhluktova, Igor Zolotovskii, Elena Obraztsova, and Vladimir Tsvetkov

Doc ID: 345966 Received 24 Sep 2018; Accepted 31 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: We demonstrate an all-fiber 2-µm holmium-doped laser hybrid mode-locked by the co-action of nonlinear polarization evolution and absorption saturation of single-walled carbon nanotubes (SWCNTs). The laser was pumped by a continuous wave Ytterbium-doped fiber laser at a wavelength of 1125 nm. Holmium laser generates 1.4 ps soliton pulses at a wavelength of 2082 nm with bandwidth up to 3.3 nm and repetition rate of 14.9 MHz. An average output power of 4.7 mW was obtained corresponding to the pulse energy up to 0.3 nJ and a peak power of 220 W.

Even and odd harmonics-enhanced supercontinuum generation in zinc-blende semiconductors

Rosvaldas Suminas, Agne Marcinkeviciute, Gintaras Tamosauskas, and Audrius Dubietis

Doc ID: 345955 Received 14 Sep 2018; Accepted 31 Oct 2018; Posted 01 Nov 2018  View: PDF

Abstract: We report on even and odd harmonics-enhanced supercontinuumgeneration in polycrystalline ZnS and ZnSe samples, as pumped byfemtosecond mid-infrared pulses. We demonstrate that efficientgeneration of multiple harmonics takes place due to random quasiphase matching, which is an intrinsic property of polycrystallinestructure and which supports multiple simultaneous three-wavemixing processes over a broad wavelength range. More specifically,using sub-μJ, 60 fs, 3.6 μm input pulses we measuredmultioctave supercontinuum spectra spanning the 0.4-5 μm and0.5-5 μm wavelength ranges in ZnS and ZnSe samples of few mmthickness, respectively. Even and odd harmonics up to 10th orderin ZnS and up to 8th order in ZnSe were recorded with the inputpulses at 4.6 μm. In contrast, filamentation in ZnTe singlecrystal is shown to produce only a moderate spectral broadening,which is accompanied by the generation of just second and thirdharmonics, highlighting the advantages of polycrystallinestructure of zinc-blende semiconductors for the generation ofultrabroadband radiation.

Simple guidelines to predict self-phase modulation patterns

Christophe Finot, Sonia Boscolo, and Frédéric Chaussard

Doc ID: 342339 Received 14 Aug 2018; Accepted 30 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: We present a simple approach to predict the main features of optical spectra affected by self-phase modulation (SPM), which is based on regarding the spectrum modification as an interference effect. A two-wave interference model is found sufficient to describe the SPM-broadened spectra of initially transform-limited or up-chirped pulses, whereas a third wave should be included in the model for initially down-chirped pulses. Simple analytical formulae are derived, which accurately predict the positions of the outermost peaks of the spectra.

Shot-to-shot performance analysis of an all-fiber supercontinuum source pumped at 2000 nm

Grzegorz Sobon, Robert Lindberg, Valdas Pasiskevicius, Tadeusz Martynkien, and Jaroslaw Sotor

Doc ID: 345685 Received 17 Sep 2018; Accepted 30 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: In this paper we report an all-fiber supercontinuum source pumped with ultrashort pulses at 1.9-2.0 μm, covering over an octave (1200-2400 nm). We investigated the shot-to-shot stability of the supercontinuum generated in a commercially-available highly nonlinear fiber (HNLF) of different lengths, ranging from 5 to 80 cm, by employing the dispersive Fourier transform method. Our study shows that using shorter HNLFs significantly improves the shot-to-shot stability while maintaining the broad spectral coverage. The supercontinuum generated in HNLFs shorter than 10 cm is characterized by excellent stability, despite the anomalous-dispersion characteristic of the fiber. The presented source is characterized by exceptional simplicity, showing readiness for outside-of-lab applications.

General model of DPAL output power and beam quality dependence on pump beam parameters: Experimental and theoretical studies

Ilya Auslender, Eyal Yacoby, Boris Barmashenko, and Salman Rosenwaks

Doc ID: 344372 Received 27 Aug 2018; Accepted 29 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: A general model that reproduces the output parameters of diode-pumped alkali lasers with different pump beam apertures and shapes is reported. Comprehensive experimental and theoretical parametric studies of static diode-pumped Cs lasers are presented, including the dependence of the output laser power and the beam quality factor on the power of the pump beam for different shapes of the pump beam, pump-to-laser beam overlaps and laser cell lengths. Two different pump lasers with circular and rectangular beam shapes and pump power of 65W and 7W, respectively, were used in two sets of experiments. An optical model of multi-transverse mode operation of alkali vapor lasers [Auslender et al, Opt. Express 25, 19767 (2017)] was modified and applied to the experimental results. The values of the laser power and M2 predicted by the model are in good agreement with the measured values for a wide range of the laser parameters.

Tunable high-average-power optical parametric oscillators near 2 μm

Chaitanya Kumar Suddapalli, Biplob Nandy, Josep Canals Casals, Hanyu Ye, and Majid Ebrahim-Zadeh

Doc ID: 341308 Received 01 Aug 2018; Accepted 29 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: We report on the development of high-average-power nanosecond and picosecond laser sources tunable near 2 μm based on optical parametric oscillators (OPOs) pumped by solid-state Nd:YAG and Yb-fiber lasers at 1.064 μm. By exploiting a 50-mm-long MgO-doped lithium niobate (MgO:PPLN) as the nonlinear crystal and operating the OPO in near-degenerate doubly-resonant configuration with intracavity wavelength selection elements, we have generated tunable high-average-power radiation across 1880-2451 nm in high spectral and spatial beam quality with excellent output stability. In nanosecond operation, pumping with a Q-switched Nd:YAG laser and using an intracavity prism for spectral control, we have generated more than 2 W of average power in pulses of 10 ns duration at 80 kHz repetition rate in narrow linewidth (<3 nm), with M2<2.8, and a passive power stability better than 2.2% rms over 1 hour. In picosecond operation, pumping with a mode-locked Yb-fiber laser and using a diffraction grating as the wavelength selection element, we have generated more than 5 W of average power in pulses of 20 ps at 80 MHz repetition rate in narrow bandwidth (~2.5 nm), with M2<1.8 and a passive power stability better than 1.3% rms over 2 hours. The demonstrated sources represent viable alternatives to Tm3+/Ho3+-doped solid-state and fiber lasers for the generation of high-power radiation in the ~2 μm spectral range.

Light scattering in Eu3+-doped glass-ceramics containing SrIINbIVO3 nanocrystals

Mikhail Shepilov, Gangadharini Upender, Olga Dymshits, and Alexander Zhilin

Doc ID: 344995 Received 05 Sep 2018; Accepted 28 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Wavelength dependence of light extinction coefficient in Eu3+-doped glass-ceramics containing SrIINbIVO3 nanocrystals is studied experimentally. In a wide spectral range, this dependence is described by the power law with the constant exponent (–p) and is attributed to light scattering. The samples containing nanocrystals demonstrate the values of p which are appreciably greater than 4. This phenomenon known as anomalous light scattering in nanostructured glasses contradicts the generally accepted opinion that p ≤ 4 for glass-ceramics. The present study enlarges the group of nanostructured glasses exhibiting anomalous light scattering.

Nonlinear propagation characters of THz multi-Gaussian beams in collisionless plasmas

Ying Wang, Yonggan Liang, Jingfeng Yao, Chengxun Yuan, and Zhongxiang Zhou

Doc ID: 337951 Received 06 Jul 2018; Accepted 28 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: The nonlinear propagation characters of the THz multi-Gaussian beam in homogeneous and inhomogeneous collisionless plasmas are theoretically explored. The equation of the dimensionless beam width parameter is derived from stationary wave equation by WKB method and paraxial ray theory. By numerically solving the differential equation, the relative beam width and intensity of the multi-Gaussian beam along the propagation have been presented. The dependences of the spot oscillation characters on the eccentric displacement, the initial beam intensity, the incident beam frequency and the plasmas electron density have been studied and compared. For inhomogeneous plasmas, the electron density increase or decrease is modeled by tanh function. The unstable propagation characters have been obtained and the effect of electron density variation rate has been discussed.

Millimiter-Structured Nondiffracting Surface Beams

Leonardo Ambrosio

Doc ID: 341101 Received 30 Jul 2018; Accepted 26 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: A new type of scalar nondiffracting beam is presented whose main feature is the freedom on the choice of a two-dimensional spatial intesity pattern dependent upon the longitudinal coordinate. Examples of such millimeter-structured surface beams are provided over Cartesian and cylindrical planes and, motivated by the idea of developing beams capable of simultaneous manipulation, guidance and/or trapping of micro- and millimeter-sized particles, here we also derive analytical expressions for their beam shape coefficients in the framework of the generalized Lorenz-Mie theory, a first step towards the analysis of light-matter interactions with spherical particles from such light fields.

Design of a Vanadium Dioxide-Based Dual-Polarization Optical PAM4 Modulator

Mehdi Miri, Sohrab Mohammadi-Pouyan, and Mohammad Hossein Sheikhi

Doc ID: 342274 Received 13 Aug 2018; Accepted 26 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: CMOS compatibility and large variations in optical properties of the vanadium dioxide (VO2) during its insulator-metal phase transitions have made this material an interesting choice for the realization of optical modulators in the silicon on insulator platform. However, despite its promising properties, the phase transition time of the electrically actuated VO2 is in the order of nanoseconds which limits the maximum achievable bit rate of the VO2 based optical modulators. To overcome this limitation and increase the maximum bit rate of the VO2 based optical modulators, the implementation of dual-polarization four-level pulse amplitude (PAM4) modulation is proposed here as a viable solution. In the design process of the dual-polarization PAM4 modulator, a VO2 based double slot waveguide is proposed, which by adjusting its geometrical parameters, can support single transverse electric (TE) or single transverse magnetic (TM) mode. For each polarization, the optical mode of the designed waveguide can provide four different propagation loss levels based on the conduction phase of its VO2 layers. Designed TE and TM waveguides are then coupled to a silicon access waveguide in a directional coupler structure to form the dual-polarization optical PAM4 modulator at the telecommunication wavelength of 1.55μm. The geometrical parameters of TE and TM waveguides and those of the coupling region are optimized so that equally spaced output power levels can be achieved in four operating states of the designed modulator in both TE and TM polarization. The required actuating voltages of the proposed modulator for TE and TM polarizations are calculated to be 8 and 3 volts, respectively, and the overall footprint of the modulator along with the required electrical contacts is estimated to be 220μm2. Numerical simulations based on three-dimensional finite-difference-time-domain (3D FDTD) method show the energy consumption of 33 fJ/bit and 121 fJ/bit for TM and TE polarizations, respectively, while the implementation of the dual-polarization PAM4 modulation scheme increases the modulation bit rate of the proposed modulator by factor of four compared to the previously reported VO2 based optical modulators.

An iterative phase retrieval algorithm for reconstruction of two arbitrary interfering fields

Roghayeh Yazdani and Hamid Fallah

Doc ID: 346543 Received 21 Sep 2018; Accepted 24 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We present a simple and robust method to simultaneously reconstruct two unknown interfering fifields. A set of the interference intensities is used in an iterative phase retrieval algorithm to recover both phase and amplitudeinformation of interfering fifields. Numerical simulations are presented to validate the proposed method. Our results show the success of this method even under noisy conditions and in the presence of phase vortices.

Numerical investigation of an ultra-broadband coherent infrared supercontinuum in a novel chalcogenide AsSe2-As2S5 multimaterial photonic crystal fiber

Mbaye Diouf, Ahmadou Wague, and Mourad Zghal

Doc ID: 346171 Received 17 Sep 2018; Accepted 24 Oct 2018; Posted 24 Oct 2018  View: PDF

Abstract: In this paper, we report on the simulation of an ultra-broadband supercontinuum (SC) extending from 1.25 to 20 µm generated using a novel AsSe2-As2S5 multimaterial photonic crystal fiber (PCF). The proposed fiber is composed of a core made of AsSe2 glass and a surrounding cladding made of As2S5 glass. The hybrid PCF is designed to have a zero dispersion wavelength (ZDW) of 3.3 µm with an overall highly engineered group velocity dispersion shifted to the mid-infrared wavelength region. The SC is generated by pumping 50 fs pulses at 4 µm emitted from an optical parameter amplifier with low energy of 0.625 nJ. The pumping wavelength is chosen in the anomalous dispersion regime close to the ZDW. The widening of the SC is mainly based on the soliton effects in the anomalous dispersion region combined with self-phase modulation, cross-phase modulation, stimulated Raman scattering, four wave mixing and dispersive wave. The obtained SC shows a high degree of coherence and a 15 fs temporal compressed pulse is generated in only 5 mm-long AsSe2-As2S5 hybrid PCF. The power proportion of the SC generated beyond 4 µm is 98 % with its long wavelength edge up to 20 µm. To the best of our knowledge, the obtained SC is the first broadest spectrum reported in the Mid-infrared region with very low energy. Our results highlight the potential of the novel chalcogenide AsSe2-As2S5 multimaterial PCF to emit across the ultra-broadband infrared atmospheric windows and the molecular fingerprint region.

High harmonic generation from a two-dimension square lattice by a circularly polarized laser pulse

Jianghua Luo and Fujun Chen

Doc ID: 344362 Received 27 Aug 2018; Accepted 23 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We investigate the high harmonic generation from a two-dimension square lattice driven by a circularly polarized laser field. The harmonic spectra with $ 4k\pm 1 $ orders are obtained by numerically solving the time-dependent Schr\"{o}dinger equations with a two-dimension periodic potential. It is found that the resulting harmonics are (nearly) circularly polarized in the low orders and are elliptically polarized in the plateau. The helicities of neighbouring-order harmonics are alternant. By varying the wavelength and field strength of the driving laser pulse, we find that the cutoff energy of the harmonic spectrum from solids in a circularly polarized laser field exhibits a linear dependence on both of the wavelength and field strength, which is similar to the conclusion obtained from the linearly polarized laser field. Our results deepen the understanding of ultrafast electron dynamics in solids driven by circularly polarized laser fields.

Linkage of photodarkening parameters to microscopic quantities in Yb-doped fiber material

Martin Leich, Ulrich Röpke, and Sylvia Jetschke

Doc ID: 346883 Received 28 Sep 2018; Accepted 23 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: We present a microscopic model that adequately describes experimental experiences of photodarkening (PD) investigations and is based on appropriate micro-optical mechanisms. The PD effect is treated as a relaxation process of a statistical ensemble of micro-optic centers (PD complexes) that are reversibly converted into color centers by the energy of pump photons, causing the measurable PD loss. The measurement parameters prove to be fundamental for the dynamics and statistics of the PD complexes and thus have a deeper physical or statistical significance. Our model is based on measurements on pristine fiber samples. Its performance is supported by its applicability to relaxation processes in non-pristine samples.

Theory of SHG in a medium with combined nonlinear response

V. Trofimov, Dmitry Kharitonov, and Mikhail Fedotov

Doc ID: 330987 Received 04 May 2018; Accepted 21 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Second-harmonic generation (SHG) is used in many practical applications such as a substance diagnostics, imaging of various processes as well as for frequency conversion. It is well known that the frequency doubling is also used for a generation of tripled frequency wave due to mixing of optical radiation at basic frequency with optical radiation at the doubled frequency. In this case, the relationship between phases of interacting waves with the basic frequency and doubled frequency plays an important role. Therefore, solution of the corresponding problem for waves phase evolutions is an urgent problem. In this paper we provide such a solution for the SHG of high intensity femtosecond pulse taking into account the influence of a cubic nonlinear response on the frequency doubling by using an original approach together with long pulse duration approximation and plane wave approximation. The main feature of our approach is absence of using the basic wave energy non-depletion approximation. In contrast to pioneering paper published by N. Bloembergen [2], we find out the explicit solution of the corresponding equations, which can not be solved using the Bloembergen's approach. Moreover, we derive an evolution of phases: for basic wave and for the wave with doubled frequency, as well as for phase difference of interacting waves. It should be stressed that the frequency conversion under consideration possesses multi-stability: there are many modes of SHG efficiency. We derive the wave intensity and phase evolution for both interactive waves for each of the modes. The derived formulas are verified by computer simulation based on using the corresponding nonlinear Schrödinger equations. It is very important that we demonstrate the robustness of the derived formulas for the shaping pulse. They can be applied for computing of the pulse shapes even if the reverse energy conversion occurs. Therefore, our approach is applicable for computing of pulse shapes and beam profiles of the interacting waves at SHG process. As an example, we consider SHG from an incident Gaussian pulse with basic frequency.

Ultrabroadband supercontinuum generation through filamentation in lead fluoride crystal

Yang yuxia, wanjun bi, Xia Li, Meisong Liao, Weiqing Gao, Yasutake Ohishi, Yongzheng Fang, and Yigui Li

Doc ID: 341889 Received 08 Aug 2018; Accepted 05 Oct 2018; Posted 09 Oct 2018  View: PDF

Abstract: We report the filamentation and supercontinuum generation of femtosecond pulse in a piece of bulk lead fluoride (PbF2) crystal with high bandgap and ultra-broadband frequency window covering 5.6 octaves. A broadband supercontinuum spanning 4.7 octaves from 350 to 9000 nm is demonstrated. The filament traces and bright conical visible emission patterns of the supercontinuums are observed. Additionally, simulations are performed to investigate the supercontinuum generation in the PbF2 crystal by using waveguide model which considers the supercontinuum generated in the filamentation as a pulse propagated process in the waveguides writing by filamentation. The findings of this study demonstrated that PbF2 crystal is a very suitable nonlinear medium used for supercontinuum generation by filamentation. This is of significance for the development of ultra-broadband SC sources based on bulk media and high-peak power lasers.

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