放电泵浦XeCl激光的理论模型

本文对传输线作电源的自持放电XeCl激光进行动力学分析,给出电子能量分布玻尔兹曼方程、能量平衡方程、电子线路方程及激光振荡方程的数值解,并与实验结果作了比较。     

Suppression of relaxation oscillations in tunable fiber lasers witha nonlinear amplified loop mirror

The concept of relaxation oscillation damping in a tunable fiber laser with a nonlinear absorber or loss element is demonstrated, using a dual-cavity erbium-doped fiber laser. A nonlinear amplified loop mirror was employed as the nonlinear loss element to facilitate damping. Experimental results exhibiting complete elimination of relaxation oscillations are presented     

固体激光器弛豫振荡尖峰脉冲参数的影响因素分析

利用固体激光器的弛豫振荡的尖峰脉冲特性,设计制作了一个窄脉宽、高重复频率的脉冲激光器。其方法是通过调节脉冲电流源的电流脉冲宽度,在固体激光器刚发出第一个尖峰脉冲时即关断泵浦电流。在实验中,对影响其尖峰脉冲参数的因素进行了探索,得出了尖峰脉冲的峰值功率、脉冲宽度与泵浦电流、腔长、输出镜透过率的关系,并从原理上对其进行了定性的分析和解释。基于实验及分析得到的结果,通过调整激光器的参数,设计出的脉冲激光器峰值功率能达到8W,脉宽能达到10 ns,重复频率可以达到百kHz的量级。文中的实验和分析结果对于固体激光器弛豫振荡的尖峰脉冲特性的理论认识及利用固体激光器弛豫振荡特性来设计脉冲激光器的参数设计都具有一定的指导意义。     

Effects of high density pumping on relaxation oscillations and mode spectra in lasers

Effects of high density pumping on relaxation oscillations and mode spectra are investigated in LiNdP4O12(LNP) lasers. It is shown that high density pumping reduces the spatial population inhomogenuity, which is due to periodic inversion saturation by a first lasing mode in the crystal, and results in spontaneous single longitudinal mode oscillations even at high excitation rates. Physical interpretations are given for single-mode operations on the basis of Auger recombination (annihilation) process for 1.048 and 1.32 μm quantums in LNP lasers. An effective diffusion parameter of excited states is shown in an increase with absorbed pump power density through the Auger process. Observed relaxation oscillation waveforms, which disagreed with the traditional laser dynamic theory, are found to be explained well by the rate equations, including the effective diffusion constant.     

Analysis of the effects of external injection and diffusion of excited states on relaxation oscillations in lasers

Effects of external injection and diffusion of excited states on the dynamics of the directly pulse-modulated laser are analyzed theoretically by examining the characteristics of the equilibrium state of the laser oscillation according to the method of Lyapunov. The analogy between relaxation oscillations in the electronic circuit and those in the directly modulated laser is discussed by introducing an equivalent circuit.     

Return-beam-induced oscillations in self-coupled semiconductor lasers

When a stripe-geometry heterostructure GaAlAs laser is irradiated by its own output beam, oscillations in the 1?100 MHz range are generated in the laser, and the frequency f of the oscillation varies with the length 2L of the optical path of the beam returned as f = ?(c/2L), with ? ? 1, where c is the velocity of light.     

Relaxation oscillations in quasi-single-mode semiconductor lasers

The intensity-relaxation-oscillation (RO) and damping rates, and the laser linewidth are measured and analyzed for a semiconductor laser under quasi-single-mode conditions. The RO frequency and the laser-linewidth dependence on laser power are measured, and are described well by the Henry single-mode theory. The relaxation-oscillation damping rate, however, shows a significant deviation from the expected power dependence, and is found to depend on the effective number of idle modes, and the fraction of energy in such modes. The observation is explained very well by a generalized quasi-single-mode theory that accounts for the collective contribution of the idle modes     

Simultaneous oscillations of different transitions in lasers

Rate equations for multitransition lasers were investigated theoretically and the effect of fluorescence properties of multilevel lasers on laser performance was examined. Simultaneous oscillations of different transitions (MTO) were found to occur due to the difference in resonator loss for individual transitions. Conditions for single transition laser oscillations (STO) as well as oscillation states in MTO were obtained. Experiments were carried out using LiNdP4O12lasers and MTO was obtained in⁴F_{3/2}(1) rightarrow⁴I_{11/2} (1, 2, 3)transitions. Dependence of oscillation states on various laser parameters was given. The oscillation mode spectra and output waveform of MTO lasers were also presented.     

Suppression of feedback oscillations in free-electron lasers

The suppression of feedback oscillations in a free-electron laser (FEL) oscillator has been investigated. It is found, through numerical simulation that a narrow attenuating strip inserted in a waveguide will not reduce FEL performance at the desired frequency and will attenuate feedback oscillations. Simulations are presented for a 5-mm-wavelength FEL with a 40-dB attenuator inserted in the interaction region     

Relaxation oscillations of quantum dot lasers

The relaxation oscillation frequency of quantum dot lasers is modelled theoretically. Its dependency on the driving current, maximum gain, intersublevel relaxation time and homogeneous broadening is investigated. For suitable, feasible quantum dot laser parameters, relaxation oscillation frequencies up to 10 GHz are predicted. Making these devices useful for 5 Gbit/s communication systems     

Relaxation oscillations in distributed feedback gas lasers

A systematic study of the relaxation oscillations in a waveguide distributed feedback gas laser equipped with a metal waveguide of rectangular cross section is presented. Approximate formulas for weak as well as strong coupling regions relating the damping rate and frequency of the relaxation oscillations to the structure parameters for this kind of laser are derived. The influence of the gain saturation on parameters describing the relaxation oscillations is shown     

Relaxation oscillations in optically pumped molecular lasers

We report the observation of relaxation oscillations in both the C¹³H3F and C¹²H3F optically pumped lasers. Expressions are derived for the oscillation frequency and its temperature and pressure dependences using a four-level rate equation model. We observe excellent agreement between measured frequencies and the theory presented. Models are considered for using this phenomenon to determine the rotational and vibrational relaxation mechanisms of the laser gases.     

Continuous microwave oscillations in GaAs junction lasers

Microwave oscillations produced by continuously operating GaAs stripe geometry junction lasers are reported here for the first time. These oscillations have been measured both in the light output of the diodes and in the dc current applied to the laser connections. The frequency of the oscillation lies in the 0.5- to 3.0-GHz range and depends strongly on current and temperature. The frequency typically increases with increasing current at a rate of 15 to 20 MHz/mA and decreases with increasing temperature at 100 to 150 MHz/°K. Introduction of an external microwave signal locks the frequency of the oscillation and reduces the oscillation width from 10 MHz to the external signal width. The frequency of oscillation agrees with a theory of intensity fluctuations in lasers based on the rate equations.     

Relaxation oscillations in waveguide distributed feedback lasers

The authors present an analysis of relaxation oscillation in planar and fiber distributed feedback lasers taking into account end reflectivity. The laser characteristics obtained as a function of the system parameter show competition between two different resonators (Fabry-Perot and distributed) as well as the influence of the gain saturation on the parameters describing relaxation oscillations     

Intraband relaxation time in quantum-well lasers

Intraband relaxation time, which causes spectral broadening of optical gain and spontaneous emission spectra, is estimated theoretically for quantum-well lasers. Carrier-carrier and carrier-longitudinal-optical (LO) phonon scattering mechanisms are considered, and it is shown that hole-hole, electron-hole, and hole-LO phonon scattering are dominant in spectral broadening. Intraband relaxation time determined by all of these mechanisms increases slightly with the decrease of well width. The dependence of intraband relaxation time on temperature, carrier density, and energy of electron and hole is also shown. Spectral line shape is discussed as an extension of the above calculation, and an approximated formula is given     

Spectral signature of relaxation oscillations in semiconductorlasers

A novel and relatively simple expression is given for the optical spectrum of a single-mode semiconductor laser which, due to the presence of relaxation oscillations, consists of a strong central line with a broad weak sideband at each side. The coupling between phase and amplitude fluctuations is included in this derivation and is shown to result in an asymmetry between the relaxation oscillation sidebands. This asymmetry can be used to determine the linewidth enhancement factor. Using optical heterodyne detection, the spectrum of a Fabry-Perot-type AlGaAs laser has been measured as a function of output power. Information on the dynamics of the relaxation oscillations was thus obtained. The power dependence of the frequency and damping of the relaxation oscillations allowed the spontaneous lifetime and the dependence of the gain on both carrier density (differential gain) and intensity (gain saturation) to be separately determined     

Carrier energy relaxation time in quantum-well lasers

Carrier energy relaxation via carrier-polar optical phonon interactions with hot phonon effects in multisubband quantum-well structures is theoretically studied by using both bulk longitudinal optical phonons and confined longitudinal optical phonons. We find that the width and the depth of quantum wells only have moderate effects on carrier energy relaxation rates. Our results also indicate that the difference of energy relaxation rates between the quantum well and the bulk material is not significant. We investigate the effects of longitudinal optical phonon lifetimes on the carrier energy relaxation rate. Neglect of the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time; this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficient due to carrier heating. The implications of our theoretical results in designing high-speed quantum-well lasers are discussed     

LSA relaxation oscillations in a waveguide iris circuit

Large-signal computer simulations of GaAs LSA relaxation oscillations in an X-band waveguide iris circuit are presented. The study is focused on a particular oscillator and a realistic model of an experimental circuit is used. However, the results are typical for other LSA relaxation oscillators. Basic features of the microwave circuit, characteristic voltage and current waveshapes, frequency tuning with bias voltage, and oscillator starting transients are discussed. The RF output power is shown to build up in less than ten cycles. Circuit optimization for high dc to RF conversion efficiency is discussed and circuit data for nearly 30 percent efficiency are given. Finally, efficiency degradation is discussed when doping gradients are present, and effciencies of 15 and 10 percent appear possible for doping gradients as high as 20 and 60 percent, respectively. Hence, the LSA relaxation mode is shown to be less sensitive to doping gradients than the sinusoidal LSA mode.     

Density-matrix theory of semiconductor lasers with relaxation broadening model-gain and gain-suppression in semiconductor lasers

The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by thek . pmethod and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.