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Journal of the Optical Society of America B

Journal of the Optical Society of America B

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Early Posting

Accepted papers to appear in an upcoming issue

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Articles 1 to 20 of 31 Next Page >>

October


Band-anisotropy induced Bloch-Siegert shift in graphene

  • Upendra Kumar, Vipin Kumar, Enamullah , and Girish Setlur
  • received 04/29/2014; accepted 10/14/2014; posted 10/16/2014; Doc. ID 210913
  • [full text: PDF (1650) KB)]
  • Abstract: In this work, we study the well-known phenomenon of Bloch Siegert shift paying special attention to the change in the resonance condition of anomalous Rabi oscillations that are peculiar to graphene. The inclusion of frequency doubling (counter rotating terms) in the conventional rotating wave approximation (RWA) leads to a rather small shift in the resonance condition which forms the conventional Bloch Siegert shift. In case of anomalous Rabi oscillations however, band anisotropy caused by the inclusion of next-nearest neighbor hopping together with frequency doubling or the Rashba effect leads to a Bloch Siegert shift which is quite substantial (in percentage terms, actually infinite) lending credence to the claim that the anomalous Rabi oscillation is sensitive to qualitative changes in the low energy band structure of graphene and as such is a useful indicator of the nature of quasiparticles in graphene.

Keywords (OCIS):

  • (160.4760) Materials : Optical properties
  • (190.0190) Nonlinear optics : Nonlinear optics
  • (190.4720) Nonlinear optics : Optical nonlinearities of condensed matter
  • (160.4236) Materials : Nanomaterials

Waveguiding properties of short linear chains of non-spherical metal nanoparticles

  • Ilia Rasskazov, Sergei Karpov, and Vadim Markel
  • received 09/11/2014; accepted 10/13/2014; posted 10/14/2014; Doc. ID 222807
  • [full text: PDF (626) KB)]
  • Abstract: We study numerically the discrete dispersion relations and waveguiding properties of relatively short linear chains of spherical and spheroidal silver nanoparticles. Simulations are based on Drude model for the dielectric permittivity of metal and on the dipole approximation for the electromagnetic interaction of particles. We also simulate the dynamics of femtosecond optical pulse propagation along such chains. In the case that we consider (10 particles per chain), reflections from the chain terminals play a significant detrimental role. We show that dissipative traps can be used to reduce the effects of reflections. We also show that chains composed of oblate spheroids with sufficiently small aspect ratio (nanodisks) have better waveguiding properties when compared to chains made of particles with other spheroidal shapes. This includes slower rate of decay, larger group velocity and larger bandwidth.

Keywords (OCIS):

  • (060.5530) Fiber optics and optical communications : Pulse propagation and temporal solitons
  • (240.5420) Optics at surfaces : Polaritons
  • (240.6680) Optics at surfaces : Surface plasmons
  • (250.5403) Optoelectronics : Plasmonics

Laser dynamics: Probing microscopic processes in InGaN light emitters.

  • Raymond Sarkissian, John O'Brien, and P. Daniel Dapkus
  • received 07/15/2014; accepted 10/13/2014; posted 10/14/2014; Doc. ID 216886
  • [full text: PDF (631) KB)]
  • Abstract: A measurement based on modulation response of laser cavities with InGaN quantum wells as the gain medium is proposed to study microscopic scattering rates that are of great importance when investigating the efficiency droop problem. Using semiconductor-Bloch equations, we derive an analytical equation establishing the relationship between the microscopic semiconductor processes and the modulation response of lasers. We also investigate the carrier density dependence of microscopic scattering rates by considering the correlation effects at the limit of Maxwell-Boltzmann statistics. FDTD calculations are then employed to design microdisk and photonic crystal InGaN quantum well laser cavities and the dependence of cavity quality factor to the geometry of the cavity is investigated. We further calculate, by estimation, the expected change in relaxation oscillation frequency as the cavity quality factor is varied by design.

Keywords (OCIS):

  • (140.5960) Lasers and laser optics : Semiconductor lasers
  • (230.3670) Optical devices : Light-emitting diodes
  • (350.4238) Other areas of optics : Nanophotonics and photonic crystals

Polarization sensitive nonlinear light scattering and optical limiting in aqua suspension of detonation nanodiamond

  • Viatcheslav Vanyukov, Gennady Mikheev, Tatyana Mogileva, Alexey Puzyr, Vladimir Bondar, and Yuri Svirko
  • received 08/28/2014; accepted 10/11/2014; posted 10/14/2014; Doc. ID 221869
  • [full text: PDF (1385) KB)]
  • Abstract: We report on the polarization dependence of the optical limiting (OL) and nonlinear light scattering in nanodiamond clusters suspended in distilled water. The nanosecond Z-scan measurements at wavelength of 532 nm reveal that the nonlinear transmittance of the suspension is independent of polarization, while the energy of the light pulses scattered at 90 degree shows a cosine-like dependence on the polarization azimuth of the incident beam. Moreover, the ratio of the energies of the vertically and horizontally polarized scattered pulses is a non-monotonous function of the input fluence. The obtained results can be explained in terms of the change of scattering centers size under the laser action and are in agreement with the predictions of the Rayleigh-Mie scattering theory.

Keywords (OCIS):

  • (190.0190) Nonlinear optics : Nonlinear optics
  • (160.4236) Materials : Nanomaterials
  • (290.5855) Scattering : Scattering, polarization

Time-frequency control of ultrafast plasma generation in dielectrics

  • Jiexi Liao and Jeremy Gulley
  • received 08/19/2014; accepted 10/08/2014; posted 10/14/2014; Doc. ID 221200
  • [full text: PDF (1473) KB)]
  • Abstract: This paper examines ultrafast laser-induced plasma generation in dielectrics by modeling ionization and pulse propagation in glass. Photo-ionization models for solids predict that the multi-photon ionization rate should increase for near UV frequencies, while the frequency dependence of a Drude-type absorption by conduction band electrons can produce a similar enhancement through impact ionization for frequencies in the infrared. Presented simulations reveal how these different frequency dependencies influence plasma formation during nonlinear pulse propagation in fused silica. It is further shown by a multi-rate equation model that the contribution from avalanching, when properly delayed, is reduced by an order of magnitude at near-IR frequencies. A modified multi-rate equation is then introduced to model combinations of ultrashort high-frequency and low-frequency pulses that can maximize plasma generation while reducing the required laser fluence.

Keywords (OCIS):

  • (190.5530) Nonlinear optics : Pulse propagation and temporal solitons
  • (190.7110) Nonlinear optics : Ultrafast nonlinear optics
  • (260.3230) Physical optics : Ionization
  • (320.7130) Ultrafast optics : Ultrafast processes in condensed matter, including semiconductors

Modulation instability in the oppositely directed coupler with a quadratic nonlinearity

  • Jinggui Zhang, Xiaoyu Dai, Lifu Zhang, Yuanjiang Xiang, and Yongfan Li
  • received 06/12/2014; accepted 10/08/2014; posted 10/08/2014; Doc. ID 214006
  • [full text: PDF (1516) KB)]
  • Abstract: We investigate modulation instability (MI) in nonlinear oppositely directed coupler with a quadratic nonlinearity, where one channel is made from an ordinary positive-index material (PIM) and another channel is fabricated from a negative-index material (NIM), trying to identify the different MI properties from those in conventional parametric gap system with grating. Both the analytic continuous wave (CW) solutions and dispersion relation are obtained. By using standard linear instability we in detail discuss how the ratio of the backward to forward propagating wave’s power, the phase mismatch and the ratio of coupled coefficient influence on the dynamical behavior of MI. Large stable regions are found if the fundamental harmonics (FH) falls in the normal dispersion, when compared to the case in the conventional Bragg grating with a quadratic nonlinearity where the CW solutions are unstable in most cases. In addition, we also observe the large stable regimes of the CW solutions even when the coupled strength for the second harmonics (SH) weaker than that of the FH. These findings suggest that the oppositely directed coupler with a NIM channel provides more ways to manipulate MI and soliton.

Keywords (OCIS):

  • (190.0190) Nonlinear optics : Nonlinear optics
  • (190.3100) Nonlinear optics : Instabilities and chaos
  • (160.3918) Materials : Metamaterials

(LIM2014) Micromachining of borosilicate glass surfaces using femtosecond higher-order Bessel beams

  • Weibo Cheng and Pavel Polynkin
  • received 09/03/2014; accepted 10/07/2014; posted 10/07/2014; Doc. ID 221427
  • [full text: PDF (1254) KB)]
  • Abstract: We report experimental results on micromachining of borosilicate glass slides with femtosecond higher-order Bessel beams. Transverse intensity profiles of these beams comprise concentric rings that are maintained over extended linear focus zones, facilitating machining geometries with large working distances and high aspect ratios. Both single-shot and multi-shot front-surface machining and multi-shot back-surface processing are experimentally investigated. Material removal in the latter case is furnished through the immersion of back side of the glass slide in water. Under certain conditions, we observe evidence of self-focusing and azimuthal breakup of the initially smooth ring intensity features of the beams near the glass-water interface. These beam dynamics result in the formation of beaded ring features on the back surface of the glass slide. In the case of multi-shot front-surface machining, pillar-like structures can be fabricated.

Keywords (OCIS):

  • (140.3300) Lasers and laser optics : Laser beam shaping
  • (140.3390) Lasers and laser optics : Laser materials processing
  • (190.7110) Nonlinear optics : Ultrafast nonlinear optics

Modulation instability in array of positive and negative index waveguides

  • Lingling Zhang, Yuanjiang Xiang, Xiaoyu Dai, and Shuangchun Wen
  • received 09/11/2014; accepted 10/07/2014; posted 10/16/2014; Doc. ID 222167
  • [full text: PDF (3449) KB)]
  • Abstract: The dispersion relation and modulation instability (MI) of array of alternating positive-index material (PIM) and negative-index material (NIM) waveguides are investigated. It is found that the transverse wave vector of the stability wave solution has modulation on the linear part of the dispersion relation, which leads to the dispersion relation is linear on staggered case. The MI region for staggered case is larger than the unstaggered case, which is same as that of conventional waveguide array. Whether on staggered case or on unstaggered case, the self-focusing or self-defocusing nonlinear property of PIM and NIM channels affects the gain value of the array, and the gain structure of the array for unstaggered case has important dependence on the nonlinear property of PIM and NIM channels, but do not affected by the nonlinear property of them for the staggered case. It is also found that except the nonlinear property of the channels, the interaction of the nonlinear effect of them also has great influence on the generation of the MI. These findings indicate that we can manipulate MI in array of positive and negative index waveguides with the controllability of NIM channel.

Keywords (OCIS):

  • (190.0190) Nonlinear optics : Nonlinear optics
  • (190.3100) Nonlinear optics : Instabilities and chaos
  • (190.5530) Nonlinear optics : Pulse propagation and temporal solitons

Topology optimization of simultaneous photonic and phononic bandgaps and highly effective phoxonic cavity

  • Hao-Wen Dong, Yue-Sheng Wang, Tian-Xue Ma, and Xiao-Xing Su
  • received 09/05/2014; accepted 10/05/2014; posted 10/06/2014; Doc. ID 222523
  • [full text: PDF (1332) KB)]
  • Abstract: By using the non-dominated sorting-based genetic algorithm II, we study the topology optimization of the two-dimensional phoxonic crystals (PxCs) with simultaneously maximal and complete photonic and phononic bandgaps. Our results show that the optimized structures are composed of the solid lumps with narrow connections, and their Pareto-optimal solution set can keep a balance between photonic and phononic bandgap widths. Moreover, we investigate the localized states of PxCs based on the optimized structure and obtain structures with more effectively multimodal photon and phonon localization. The presented structures with highly focused energy are good choices for the PxC sensors. For practical application, we design a simple structure with smooth edges based on the optimized structure. It is shown that the designed simple structure has the similar properties with the optimized structure, i.e. simultaneous wide phononic and photonic bandgaps and a highly effective phononic/photonic cavity.

Keywords (OCIS):

  • (160.1050) Materials : Acousto-optical materials
  • (220.4880) Optical design and fabrication : Optomechanics
  • (350.7420) Other areas of optics : Waves
  • (160.5298) Materials : Photonic crystals

Reflective Vertical Cavity Quantum-Wells Saturable Absorber as an All-Optical Nonlinear Phase-Shifting Element

  • R. Pradhan, S. Saha, and P. K. Datta
  • received 06/18/2014; accepted 10/03/2014; posted 10/10/2014; Doc. ID 214325
  • [full text: PDF (698) KB)]
  • Abstract: A scheme of all-optical nonlinear phase-shifting element (NPE) is proposed, based on a reflective vertical cavity semiconductor (quantum wells) saturable absorber (R-VCSSA). The nonlinear round-trip phase-shift in a low-intensity resonant VCSSA is obtained at an input intensity due to the saturating nonlinearity in index change and optically induced thermal effects. An enhanced large nonlinear positive or negative phase-shift incurred in a reflected signal is investigated analytically with the wavelength tuning of the probe signal around the low intensity resonant wavelength of the Fabry-Perot (F-P) cavity. The device may be useful in compensating phase of a signal, either positive or negative, in long-haul fiber communications. A representative InGaAs/InP quantum wells based VCSSA is considered in the pump-probe configuration. At pump power of 17.89mW, a maximum phase-shift of –0.68radian and +0.46radian is observed at the probe wavelength of 1557nm and 1564nm, respectively.

Keywords (OCIS):

  • (040.4200) Detectors : Multiple quantum well
  • (050.2230) Diffraction and gratings : Fabry-Perot
  • (050.5080) Diffraction and gratings : Phase shift
  • (190.0190) Nonlinear optics : Nonlinear optics

Polarization dynamics induced by orthogonal optical injection close to the lasing mode of a single-transverse mode VCSEL

  • Pablo Perez, Hong Lin, Angel Valle, and Luis Pesquera
  • received 08/01/2014; accepted 10/02/2014; posted 10/06/2014; Doc. ID 220272
  • [full text: PDF (1994) KB)]
  • Abstract: We investigate experimentally polarization-resolved nonlinear dynamics of a long-wavelength single-transverse mode vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection. We focus on the case in which the wavelength of the optical injection is close to the wavelength of a free-running VCSEL characterized by large values of the birefringence parameter. We observe an elliptically polarized injection locked (EPIL) state. The EPIL region is measured in the frequency detuning-injected power plane. Above the upper boundary of the EPIL region the nonlinear dynamics of the system is usually characterized by periodic oscillations of the power of both linear polarizations at a frequency close to the relaxation oscillation frequency of the VCSEL or one half of this value. Below the lower boundary of the EPIL region the VCSEL operates in the parallel polarization and demonstrates periodic pulsations at a frequency given by the frequency detuning or one half of this value. Our results confirm the theoretical predictions of Sciamanna et al.

Keywords (OCIS):

  • (140.3520) Lasers and laser optics : Lasers, injection-locked
  • (190.3100) Nonlinear optics : Instabilities and chaos
  • (140.7260) Lasers and laser optics : Vertical cavity surface emitting lasers

Extracting Dynamical Green’s Function of Ultracold Quantum Gases via Electromagnetically Induced Transparency

  • H. H. Jen and Daw-Wei Wang
  • received 07/23/2014; accepted 10/01/2014; posted 10/06/2014; Doc. ID 217586
  • [full text: PDF (429) KB)]
  • Abstract: The essential quantum many-body physics of an ultracold quantum gas relies on the single-particle Green’s functions. We demonstrate that it can be extracted by the spectrum of electromagnetically induced transparency (EIT). The single-particle Green’s function can be reconstructed by the measurements of frequency moments in EIT spectroscopy. This optical measurement provides an efficient and nondestructive method to reveal the many-body properties, and we propose an experimental setup to realize it. Finite temperature and finite size effects are discussed, and we demonstrate the reconstruction steps of Green’s function for the examples of three-dimensional Mott-insulator phase and one-dimensional Luttinger liquid.

Keywords (OCIS):

  • (020.0020) Atomic and molecular physics : Atomic and molecular physics
  • (270.0270) Quantum optics : Quantum optics
  • (270.1670) Quantum optics : Coherent optical effects
  • (020.1475) Atomic and molecular physics : Bose-Einstein condensates

September


Composite SiC/Au nanorod structure for sensing

  • Yurii Demydenko, Saulius Juodkazis, and Valeri Lozovski
  • received 07/04/2014; accepted 09/29/2014; posted 10/02/2014; Doc. ID 216308
  • [full text: PDF (831) KB)]
  • Abstract: A self-consistent theoretical model for the optical response of composite metal-dielectric nanorods on the surface of dielectric medium is developed. The modeling of optical properties of evanescent TE and TH-polarized modes in Otto configuration are presented for experimentally realizable geometries. We show an effective control of absorption spectrum of the modes by tuning the height of plasmonic metal caps on dielectric rods. Configurational resonances can explain the origin of absorption peaks caused by a surface wave excitation. These absorption resonances at infra-red spectral range due to surface phonon polaritons can be used for sensing applications similarly to the surface plasmon polaritons at visible wavelenghts. Large parameter space of spectral tunability of the surface modes is explored numerically.

Keywords (OCIS):

  • (240.6690) Optics at surfaces : Surface waves
  • (300.1030) Spectroscopy : Absorption

On the use of etalon-immune-distances to reduce the influence of background signals in frequency modulation spectroscopy and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy

  • Patrick Ehlers, Alexandra Johansson, Isak Silander, Aleksandra Foltynowicz, and Ove Axner
  • received 06/25/2014; accepted 09/29/2014; posted 10/06/2014; Doc. ID 214351
  • [full text: PDF (703) KB)]
  • Abstract: The detection sensitivity of frequency modulated techniques such as frequency modulation spectroscopy (FMS) and noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) is often limited by etalon background signals. It has previously been shown that the impact of etalons can be reduced by the use of etalon-immune-distances (EIDs), i.e. by separating the surfaces that give rise to etalons by a distance of $q\cdot L_{\rm{m}}$ where $L_{\rm{m}}$ is given by $c/2n\nu_{\rm{m•}}$, where, in turn, $n$ and $\nu_{\rm{m•}}$ are the index of refraction between the components that make up the etalon (thus most often that of air) and the modulation frequency, respectively, and where $q$ is an integer (i.e., 1, 2, 3,...) or half integer (i.e., $\sfrac{1}{2}, 1, \sfrac{3}{2},...$) for the dispersion and absorption modes of detection, respectively. An etalon created by surfaces separated by an EID will evade detection and thereby not contribute to any background signal. The concept of EID in FMS and NICE-OHMS is in this work demonstrated, scrutinized, and discussed in some detail. It is shown that the influence of EID on the absorption and dispersion modes of detection is significantly different; signals detected at dispersion phase are considerably less sensitive to deviations from exact EID conditions than those detected at absorption phase. For example, the FM background signal from an etalon whose length deviates from an EID by 2.5\% of $L_{\rm{m}}$ (e.g. by 1 cm for an $L_{\rm{m}}$ of 40 cm), detected in dispersion, is only 9\% of that in absorption. This makes the former mode of detection the preferred one whenever a sturdy immunity against etalons is needed or when optical components with parallel surfaces (e.g. lenses, polarizers, or beam slitters) are used. The impact of the concept of EID on NICE-OHMS is demonstrated by the use of Allan-Werle plots.

Keywords (OCIS):

  • (120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
  • (140.4780) Lasers and laser optics : Optical resonators
  • (300.6310) Spectroscopy : Spectroscopy, heterodyne
  • (300.6380) Spectroscopy : Spectroscopy, modulation
  • (300.6390) Spectroscopy : Spectroscopy, molecular
  • (140.3518) Lasers and laser optics : Lasers, frequency modulated

GaInAsP/InP-Based Optical Modulator Consisting of Gap-Surface-Plasmon-Polariton Waveguide: A Theoretical Analysis

  • Tomohiro Amemiya, Eijun Murai, Zhichen Gu, Nobuhiko Nishiyama, and Shigehisa Arai
  • received 07/07/2014; accepted 09/28/2014; posted 10/06/2014; Doc. ID 216529
  • [full text: PDF (2858) KB)]
  • Abstract: We propose a III-V-based electro-absorption plasmon modulator that can be used to construct fully monolithic plasmonic integrated circuits. Our device consists of a GaInAsP/InP gap-surface-plasmon-polariton waveguide with Al2O3/ITO layers on both sides of the InGaAsP core. Using this design, the intensity of transmitted light can be modulated by controlling the carrier concentration of the ITO layer, as a positive gate voltage induces electron accumulation in the ITO layer (this is similar to the operation of FinFETs). The extinction ratio was 4.5 dB/μm with a gate voltage swing of 0-5, and the insertion loss was found to be 1.5 dB/μm. The figure of merit (ratio of extinction ratio to transmission loss) is 3, a result that is far superior to other conventional Si-based plasmonic photomodulators.

Keywords (OCIS):

  • (130.0130) Integrated optics : Integrated optics
  • (250.5403) Optoelectronics : Plasmonics
  • (130.4110) Integrated optics : Modulators

Spectra of pulses propagating in atomic media in the closed double Λ configuration

  • Andrzej Raczynski, Jaroslaw Zaremba, and Sylwia Zielinska-Raczynska
  • received 08/06/2014; accepted 09/28/2014; posted 10/10/2014; Doc. ID 220532
  • [full text: PDF (459) KB)]
  • Abstract: A simultaneous propagation of two probe pulses in a medium of four-level atoms irradiated by three control fields is studied. The double Λ configuration has been closed by a fifth field, coupling the lower levels. It is shown that the propagation can be described in terms of four modes characterized by particular effective susceptibilities which have absorption or gain peaks and transparency windows. For incoming one-peak pulses, multipeak spectra are built during the propagation, including in general a few components of well-defined frequencies. They evolve along the sample, some of their spectral components being transmitted, absorbed or amplified.

Keywords (OCIS):

  • (270.1670) Quantum optics : Coherent optical effects
  • (270.4180) Quantum optics : Multiphoton processes
  • (270.5530) Quantum optics : Pulse propagation and temporal solitons

Investigation of a Quasi-3D Plasmonic Nanostructure for TE and TM polarizations

  • Afsaneh Shahmansouri and Bizhan Rashidian
  • received 07/16/2014; accepted 09/26/2014; posted 09/29/2014; Doc. ID 217000
  • [full text: PDF (1406) KB)]
  • Abstract: Quasi-3D (Q3D) plasmonic nanostructures consisting of a metallic film perforated as an array of nanoholes, separated by a gap from a nanodisks array are theoretically investigated under plane wave illumination with transverse electric (TE), and transverse magnetic (TM) polarizations. The results are compared with the results of a simple nanodisks array. A full discussion involving the couplings between plasmon resonance in nanodisks, surface plasmon polaritons (SPP) on the interfaces of metallic film, and different diffractive grating orders which contribute in the couplings, will be presented. The large difference between the plasmon behavior of the alone nanodisks array, and nanodisks array in the presence of nanoholes array will be fully investigated.

Keywords (OCIS):

  • (230.1950) Optical devices : Diffraction gratings
  • (240.6680) Optics at surfaces : Surface plasmons
  • (350.4238) Other areas of optics : Nanophotonics and photonic crystals

Electromagnetically Induced Phase Grating via Population Trapping Condition in a Microwave-Driven Four-Level Atomic System

  • Tayebeh Naseri and Rasoul Sadighi-Bonabi
  • received 07/23/2014; accepted 09/25/2014; posted 09/25/2014; Doc. ID 217116
  • [full text: PDF (975) KB)]
  • Abstract: Electromagnetically induced phase grating controlled by coherent population trapping (CPT) in a four-level Y-type atomic system is studied. The novel result indicates that the diffraction efficiency of phase grating is dramatically enhanced due to the existence of CPT condition and the diffraction efficiency up to 30% can be obtained. An interesting result is considerable due to improvement of higher order diffraction intensities via microwave driven field. It is found that the phase and amplitude of microwave field can improve the efficiency of the phase grating. The present atomic scheme takes full advantage of the microwave driven field in the experimental work for generating EIG, which induces the quantum coherence and further controls linearity and nonlinearity behaviors of the present system.

Keywords (OCIS):

  • (050.0050) Diffraction and gratings : Diffraction and gratings
  • (050.1950) Diffraction and gratings : Diffraction gratings
  • (190.0190) Nonlinear optics : Nonlinear optics

Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water

  • Carles Milian, Amelie Jarnac, Yohann Brelet, Vytautas Jukna, Aurelien Houard, Andre Mysyrowicz, and Arnaud Couairon
  • received 07/18/2014; accepted 09/24/2014; posted 09/25/2014; Doc. ID 217275
  • [full text: PDF (1309) KB)]
  • Abstract: We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\ \mu$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned.

Keywords (OCIS):

  • (190.0190) Nonlinear optics : Nonlinear optics
  • (190.4180) Nonlinear optics : Multiphoton processes
  • (260.5950) Physical optics : Self-focusing
  • (350.5400) Other areas of optics : Plasmas

Orthogonal Solutions for Asymmetric Strongly Coupled Waveguide Arrays: an elegant, analytical approach

  • Niharika Kohli, Sangeeta Srivastava, and Enakshi Sharma
  • received 05/22/2014; accepted 09/24/2014; posted 09/25/2014; Doc. ID 212621
  • [full text: PDF (1006) KB)]
  • Abstract: Silicon on Insulator (SOI) waveguides are the focus of present day nanophotonics due to their smaller device footprint and compatibility with CMOS technology. Coupled waveguide arrays have been widely analysed by the simple yet intuitive coupled mode theory. However, for asymmetric strongly coupled waveguide arrays, the supermodes obtained by coupled mode theory are not orthogonal solutions. We present an elegant, three step analytical methodology for obtaining accurate orthogonal TE solutions for asymmetric planar waveguide arrays. First, the propagation characteristics of the individual waveguides are obtained. Next, an orthogonal basis set, which is formed by a linear combination of the modal fields of the individual waveguides, is generated using the Gram Schmidt orthogonalization procedure. The Ritz Galerkin Variational method, with the trial field as an expansion in terms of the newly formed orthogonal basis set, is then used to obtain the modes of the coupled waveguide array. The procedure is illustrated by use on strongly coupled SOI waveguide arrays. The TE modal solutions obtained for the waveguide arrays are exactly orthogonal to one another. Since the new orthogonal basis set is essentially a linear combination of the modal solutions of the individual waveguides, the quantities involved in the analysis are analytically identical to those defined as coupling coefficients and overlap integrals in the conventional coupled mode theory. The theory presents itself as a strong alternative to numerically intensive and time consuming techniques that are frequently employed for the analysis of such structures.

Keywords (OCIS):

  • (130.0130) Integrated optics : Integrated optics
  • (130.2790) Integrated optics : Guided waves

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