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Impact of fourth order dispersion on modulational instabilities in asymmetrical three-core optical fiber
摘要： In this paper we investigate the impact of linear coupling coefficient and coupling coefficient dispersion on modulational instability (MI) in the presence of fourth order dispersion (FOD) in an asymmetric three core optical fiber under normal and anomalous dispersion regime. In addition, we also considered the impact of symmetric and asymmetric power ratio on MI characteristics. It is found that there is significant influence by linear coupling coefficient and frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes. In case of CCD, the impact of FOD found to be quite insensitive and found no MI gain in the absence of CCD under symmetric power ratio under coupling coefficient dispersion (CCD) on MI under different dispersion regimes. In anomalous dispersion regime, at β4 < 0 the generation of smaller MI secondary side bands were observed at higher frequencies while at normal dispersion the effect of FOD leads to breaking of MI gain at different values of coupling coefficient. Though the appearance of the MI gain at different frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes.
关键词： modulational instability,asymmetrical three-core optical fiber,fourth order dispersion,linear coupling coefficient,coupling coefficient dispersion
更新于2025-09-23 15:19:57
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Nano-wrinkles, compactons, and wrinklons associated with laser-induced Rayleigha??Taylor instability: I. Bubble environment
摘要： We study dynamics, structure and organization of the new paradigm of wavewrinkle structures associated with multipulse laser-induced RayleighTaylor (RT) instability in the plane of a target surface in the circumferential zone (C-zone) of the spot. Irregular target surface, variation of the fluid layer thickness and of the fluid velocity affect the nonlinearity and dispersion. The fluid layer inhomogeneity establishes local domains arranged (organized) in the ?domain network?. The traveling wavewrinkles become solitary waves and latter on become transformed into stationary soliton wavewrinkle patterns. Their morphology varies in the radial direction ofaussian-like spot ranging from the compacton-like solitons to the aperiodic rectangular waves (with rounded top surface) and to the periodic ones. These wavewrinkles may be successfully juxtapositioned with the exact solution of the nonlinear differential equations formulated in the KadomtsevPetviashvili sense taking into account the fluid conditions in particular domain. The cooling wave that starts at the periphery by the end of the pulse causes sudden increase of density and surface tension: the wavewrinkle structures become unstable what causes their break-up. The onset of solidification causes formation of an elastic sheet which starts to shrink generating lateral tension on the wavewrinkles. The focusing of energy at the constrained boundary causes the formation of wrinklons as the new elementary excitation of the elastic sheets.
关键词： solitary waves,nonlinear waves,Compactons,RayleighTaylor instability,wrinklons,lasermatter interaction,partial differential equations
更新于2025-09-23 15:19:57
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Modal instabilities in high power fiber laser oscillators
摘要： Transverse mode competition and instabilities in high-power fiber oscillators have been studied experimentally by monitoring the dynamic power exchanges and characteristic frequencies of the transmitted fundamental mode (FM) and scattered high-order modes (HOMs) of the fiber laser cavity under CW and pulsed pumping. The FM and HOM power evolution indicates the presence of two competing effective laser cavities which result in rich output dynamics and full chaotic operation. The thermal and inversion related contributions to the observed instabilities have been identified by monitoring the associated characteristic instability frequencies under pulsed pumping. It is shown that in the transient regime, both inversion and thermal effects contribute successively to the observed power instabilities. Increasing the pump power leads to full chaotic response through an interplay between transverse and longitudinal mode instabilities.
关键词： Transverse mode instability,inversion effects,thermal effects,high-power fiber lasers,mode competition
更新于2025-09-23 15:19:57
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Dynamic space-charge-controlled field emission model of current conduction in metala??insulatora??semiconductor capacitors
摘要： A dynamic space-charge-controlled field emission (SCC-FE) model that considers temporal insulator charge variations caused by voltage stress is developed for analyzing the current conduction in insulators in the entire voltage range of measurement, yielding good agreement between experiments and simulations. The usage of prestressed samples in this analysis is essential for accurately estimating the electron affinities of insulators, yielding 1.65 and 1.93 eV as the estimates for Al2O3 films formed on GaN by atomic-layer deposition (ALD) at 200 and 450 °C, respectively, and 1.65 and 1.83 eV for those on SiO2/Si, respectively. Through the bias instability analysis using the method developed here, the voltage-stress tolerance of both Si and GaN metal–insulator–semiconductor (MIS) capacitors with ALD Al2O3 films was found to be enhanced by the high-temperature (450 °C) ALD. The analysis also revealed the fact that the voltage-stress-induced flatband voltage shift of GaN capacitors with the high-temperature Al2O3 films is mainly caused by the Al2O3 charges near the substrate, hence providing a clue to even better bias stability of the GaN capacitors. With possible applications to other wide-bandgap semiconductor (WBGS) capacitors, the dynamic SCC-FE analysis developed here will play an essential role in analyzing not only gate insulator characteristics but also many reliability issues of various WBGS MIS field-effect transistors.
关键词： Al2O3 films,bias instability,atomic-layer deposition,dynamic space-charge-controlled field emission,metal–insulator–semiconductor capacitors
更新于2025-09-23 15:19:57
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Transportable 1555-nm Ultra-Stable Laser with Sub-0.185-Hz Linewidth
摘要： We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit (7 × 10?16) of the 10-cm ultra-low expansion glass cavity at 1–10 s averaging time and the beat signal of the two lasers reveals a remarkable linewidth of 185 mHz.
关键词： cavity-stabilized,linewidth,frequency instability,1555-nm ultra-stable laser
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Formation of Space Charge Wave with Wide Frequency Spectrum in Helical Electron Beam of Two-Stream FEL Transit Section with Longitudinal Electric Field
摘要： The longitudinal electric field effect on the formation of a space charge wave (SCW) with wide frequency spectrum in the helical two-stream relativistic electron beam (REB), which moves in transit section of multiharmonic two-stream superheterodyne free-electron laser, is analyzed. In the framework of cubic nonlinear approximation, it is shown that the use of the accelerating electric field makes it possible to increase the multiharmonic SCW width of the frequency spectrum. It is shown that the retarding electric field causes the increase of the amplitude level SCW harmonics, as well as the decrease of its saturation length.
关键词： three-wave parametric resonance,helical electron beam,two-stream instability,two-stream superheterodyne free-electron laser,longitudinal electric field
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Full-mode analysis of the plasmon oscillations of 2D electron gas subjected to electric field
摘要： Plasmon dispersion law including wave vector dependencies of the oscillation frequency, !′(q), and the damping !′′(q) of 2D electron gas subjected to the steady-state electric field were analyzed in the frameworks of general kinetic theory of collisionless plasma. Two particular cases of ungated and gated 2D electron gas were considered. We found that the spectra of 2D plasmons have the following peculiarities: multi-branched character, strong dependence of Landau damping vs dielectric surrounding of 2D gas, the strong non-reciprocal dispersion with respect to the direction of electron drift, existence of an extended instability range of wave vectors where plasmons propagating along the electron drift have essential increment of oscillations, !′′>0. Also, the effect of the mode interaction under applied field was identified.
关键词： plasmon instability,THz plasmonics,non-reciprocity,Landau damping
更新于2025-09-23 15:19:57
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Modulational instability of ultraintense laser pulses in electron-positron-ion plasmas including vacuum polarization effect
摘要： A nonlinear equation for describing the dynamics of slowly varying envelope of ultra-intense lasers in electron-positron-ion plasmas is derived, taking into account the vacuum polarization effect. Then the modulation instability of ultra-intense laser pulses in the plasmas is investigated. Theoretical results show that the growth rate of modulation instability is originated from the relativistic ponderomotive force of lasers and the vacuum polarization effect. In the regime of different physical parameters, there is an interplay of the two effects. The dependence of the growth rate on the intensity of lasers, the temperature of electrons (positrons), the component of plasmas and the vacuum polarization effect is numerically studied.
关键词： vacuum polarization,lasers,plasmas,modulational instability
更新于2025-09-23 15:19:57
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Numerical study on the laser ablative Rayleigha??Taylor instability
摘要： The laser ablative Rayleigh–Taylor instability plays an important role in the ignition of inertial re?nement fusion. An accurate simulation of this process is important to control the growth of ?ow instability during the implosion. In this paper, taking the simulations of the hydrodynamics, the laser energy deposition and the electronic thermal conductivity into consideration, a massively parallel laser ablative Rayleigh–Taylor instability code based on Euler method is developed. Some open source codes are used to improve the code development ef?ciency. The accuracy of the hydrodynamics simulation is tested by an analytical theory about the weakly nonlinear Rayleigh–Taylor instability with double interfaces. The benchmark of an one dimensional heat conductivity is used to test the accuracy of the thermal conductivity simulation. The laser ablative plane target and the laser ablative Rayleigh–Taylor instability are used to test the reliability of the code on the simulation of the whole laser ablative process. It is shown that the con?dence of our numerical simulation code is high and the code framework we designed is effective. It can be a basis on studying the problems about the laser ablative instability in inertial re?nement fusion.
关键词： Rayleigh–Taylor instability,Numerical simulation,Inertial con?nement fusion,Laser ablation
更新于2025-09-23 15:19:57
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Excitation conditions of several fundamental nonlinear waves on continuous-wave background
摘要： We study the excitation conditions of antidark solitons and nonrational W-shaped solitons in a nonlinear fiber with both third-order and fourth-order effects. We show that the relative phase can be used to distinguish antidark solitons and nonrational W-shaped solitons. The excitation conditions of these well-known fundamental nonlinear waves (on a continuous-wave background) can be clarified clearly by the relative phase and three previously reported parameters (background frequency, perturbation frequency, and perturbation energy). Moreover, the numerical simulations from the nonideal initial states also support these theoretical results. These results provide an important complement for the studies on relationship between modulation instability and nonlinear wave excitations, and are helpful for controllable nonlinear excitations in experiments.
关键词： nonlinear fiber,relative phase,nonrational W-shaped solitons,antidark solitons,excitation conditions,fourth-order effects,modulation instability,third-order effects
更新于2025-09-19 17:15:36