激光束的空间调制

本文研究了激光束的空间调制问题,得到了栅形、缝形、孔形、扇形调制器的激光束调制场分布式,给出了光强分布图,介绍了初步实验结果.     

The Eficiency of a Free-electron laser

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自由电子激光器评述

自由电子激光器是地基激光武器的首选器件。本文评述自由电子激光器的研究现状和发展动态.特别是射频自由电子激光器和感应型自由电子激光器,近年来,它们已成了世界上许多国家的主要研究对象。     

Oscillator performance and energy extraction from a KrF laser pumped by a high-intensity relativistic electron beam

A laser cell with 21 of excitation volume was used to study the electron-beam pumped KrF laser system at excitation rates of 1.8- 7.0 MW/cm³. The system was optimized as an oscillator for various mixtures of Ar, Kr, and F2at total pressures of 1000 and 2500 torr. The resulting optimum conditions gave an intrinsic efficiency (laser energy out/electron-beam energy deposited) of 12 percent for the 1000 torr total pressure mixture with an output energy of 11 J/1. An efficiency of 10 percent with an output of 40 J/1 was obtained for the 2500 torr mixture. The system was then used as an amplifier to measure the extracted power as a function of input power for the two mixtures. The small-signal gain go, the nonsaturable absorption α, and the saturation intensity Iswere determined for the two mixtures. Analysis of the data gave g0= 16-18 percent/cm,alpha = 0.75-1.25percent/cm, and Is= 2 MW/cm²for the 1000 torr mixture and g0= 17-19 percent/cm,alpha = 1.0-1.5percent/cm, andI_{s} = 9MW/cm²for the 2500 torr mix.     

CW silver ion laser with electron beam excitation

A continuous-wave (CW) laser power of 140 mW was obtained in the 840.39-nm transition of Ag II by electron-beam excitation. The electron-beam excited metal-vapor ion laser is capable of operating using metals with high vaporization temperatures, and is of interest for generation of CW coherent radiation in th 220-260-nm spectral region     

光谱合成激光阵列指向偏差的光束特性分析

保持良好光束质量的输出对实际光谱合成系统的构建至关重要。从理论上研究光纤激光阵列指向偏差对合成系统光束特性的影响,修正了带有指向偏转角激光队列的入射光场,结合光谱合成的光传输模型和统计学分析,讨论了合成激光光束质量随均匀分布随机扰动的变化规律。仿真结果表明,指向偏差对合成系统的输出特性影响显著,当激光队列的最大偏转角仅为0.05时,合成系统的光束质量就会退化到（6.491.73）。为实现合成光束亮度的定标放大,逐步扩展激光队列的阵列规模,合成系统光束质量的变化会逐渐趋于稳定,以变化稳定时的阵列规模（30路子光束）作为参考,拟合M2因子随最大指向偏转角的变化趋势。     

Nonlinear dynamics of a laser diode with optical feedback systemssubject to modulation

The nonlinear dynamic behavior of a direct frequency-modulated diode laser with strong optical feedback is examined and compared to a laser diode subject to electro-optically modulated, strong optical feedback. Direct modulation is achieved by sinusoidal modulation of the diode laser injection current. Electro-optic modulation is achieved by applying a sinusoidal voltage to an intracavity phase modulating element. The output state (characterized by the output power versus time, the intensity noise spectrum and the optical frequency spectrum) for both types of modulation is dependent on the ratio of the modulation frequency to the external cavity resonant frequency, and the modulation power. A number of distinct states are observed: conventional amplitude modulation (with FM spectra); multimode, low-noise amplitude modulation; multimode, high-noise amplitude modulation; periodic limit-cycle operation; quasi-periodicity; chaos; low-frequency fluctuations; and mode-locking. There are significant differences between the direct and electro-optic frequency-modulation cases. The onset of the dynamic instability is characterized as a noisy period-one oscillation for direct modulation and a low-frequency fluctuation for intracavity electro-optic modulation. Phase portraits produced experimentally with the use of a digital phosphor oscilloscope are shown to agree well with those constructed from output power versus time data. This represents an experimental method for examining the dynamics phase portraits in real-time     

Free electron laser annealing of silocon carbibe

We have applied a free electron laser (FEL) to crystallize amorphous silicon carbide (a-SiC) and to remove the damage and activate the dopant of a damaged layer of nitrogen implanted cubic silicon carbide (3C-SiC) films at room temperature. The FEL has two main characteristics, wavelength tunability and ultrashort-pulse operation (~10 ps) with intense peak power (~MW). The wave-length was selected at the energy of the Si-C stretch mode in order to excite the lattice vibration directly. We observed the crystallization of a-SiC occurs at room temperature when irradiation with a 12.6 μm FEL. The present results indicate that FEL annealing (12.6 μm: transverse optical mode, 10.3 μm: longitudinal optical mode) is effective for recrystallization and activation of an ion-implanted SiC films.     

光纤激光谱合成改善光束质量的研究进展

光束质量是衡量激光性能的重要指标。鉴于当前谱合成光束质量的研究现状,本文归纳出3种改善光束质量的方法：窄线宽法,双光栅色散补偿法,抑制光栅热变形法。对于每一种方法,详细介绍了其设计思路;综述了该思路下光束质量改善所取得的进展。此外,本文还展示了我们团队研究光栅热变形、影响光束质量的理论和实验成果。该成果表明：在30 W激光辐照下,2 min内,M²从1.06增加到1.26。显示出谱合成的光束质量是一个动态变化过程。     

Theory of the nitrogen laser excited by a relativistic electron beam

The 3371-Å nitrogen laser power produced by a relativistic electron beam propagating into nitrogen gas is calculated. The excitation contribution of cascade electrons is found to be negligible, compared to the excitation caused by plasma electrons drifting in the inductive electric field produced by the beam. The extensive experimental data on nitrogen are used wherever possible in the calculation, and the sensitivity of the calculation to the various input data is given. The mechanism of excitation by plasma electrons alone yields agreement within experimental uncertainty for such parameters as the peak laser power, the laser pulsewidth and delay, and the dependence of the laser power on gas pressure. For a larger drift tube radius, the plasma electron mechanism predicts higher power and a different pressure dependence, in agreement with experimental trends. In calculating the laser power, the beam propagation details, excitation to the upper and lower laser levels, collisional quenching, a threshold for amplified spontaneous emission, and excitation and deexcitation by plasma electrons are included, but coherent dipole moment effects are neglected.     

Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm³. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from theBandCstates indicate that collisional mixing between these states is very rapid. The formation efficiencies of theBandCstates are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and1.5 times 10^{-10}cm³. s^-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of1.7 times 10^{-9}cm³. s^-1was obtained for quenching by HCl, and a value ofsim 1 times 10^{-7}cm³. s^-1was estimated for electron deactivation.     

Mean electron energy in a CO2 laser plasma

It is argued that measurements made using microwave radio-metric techniques represent a true mean electron energy for the CO2 laser plasma. They agree well with some other experimental values, and excellently with a theoretically calculated value.     

Cd recombination laser in a plasma generated by an electron beam

Laser action was obtained in the 1.40, 1.43, and 1.65 μm lines of CdI following electron-ion recombination in a plasma generated by an electron beam. Lasing does not occur during the excitation pulse due to the electron impact population of the laser lower levels. In this plasma, supercooling of the electrons is achieved under stationary conditions, and efficient CW recombination laser action might also be possible on lines in which the lower level is not significantly populated by electron collisions. Seven new infrared laser lines in CdII are also reported.     

半导体激光器光束谱合成效率的分析

针对半导体激光器的光束谱合成系统结构及其特点,利用Lang-Kobayashi模型建立的速率方程,在稳态情况下,推导出单个子光束经谱合成系统后的效率公式,并进一步讨论了多个光源经谱合成系统后的合成效率及其影响因素。研究结果表明:半导体激光器经谱合成系统的效率与半导体激光器输出端面和外腔输出耦合镜的反射率的相对大小、变换透镜和望远镜系统的透过率、闪耀光栅的衍射效率以及系统的耦合效率有关;在实际工程设计中,要尽可能提高变换透镜和望远镜系统的透过率、闪耀光栅的衍射效率以及系统的耦合效率,并综合考虑系统效率和光谱稳定性的要求,对半导体激光器输出端面和输出耦合镜的反射率进行优化设计。     

Generalized electron beam matching in the free-electron laser

Three matching schemes are presented for Gaussian profile electron beams in free-electron lasers (FELs). The three different classes of matching or symmetry conditions are (1) electron beams with separate betatron matching in each plane, (2) those with aspect ratio matching, and (3) cross-matched beams. The new schemes are distinct generalizations of well-known betatron matching and include ribbon profiles. The corresponding effective energy distributions and their Fourier transforms are obtained in analytical form. An analytical kernel produces the key Fredholm integral equation that solves the initial value problem     

基于空间光调制器的艾里光束能量调制方法

艾里光束由于具有无衍射、自加速和自愈合等特性,具有重要的应用前景。本文基于空间光调制器可编程特性,提出了一种可调谐的艾里光束能量调制新方法。从理论上深入分析通过在相位图中引入一个可控的调制相位而实现了艾里光束能量调控的方法,并且量化了调制参数与能量调制范围的关系。仿真和实验结果表明通过改变调制相位可以灵活地调节光束能量分布,本文的研究有助于进一步推动艾里光束的应用。     

Frequency modulation and spectral characteristics for a 1.5?m phase-tunable DFB laser

Frequency modulation (FM) and spectral characteristics for a 1.5?m phase-tunable DFB (PT DFB) laser have been studied experimentally. As tuning current was increased, light output, lasting wavelength, FM efficiency and spectral linewidth changed periodically. The continuous-wavelength tuning range was over l.2nm (150 GHz). A high FM efficiency, more than 16GHz/mA, and a flat FM response, up to 100MHz, were obtained.     

Characteristics of the electron beam pumped iodine monofluoride laser

Electron beam pumping of Ar/CF3I/NF3mixtures yields optical pulse lengthssim0.5 mus from iodine monofluoride. Laser efficiency in this system is ∼0.04 percent. Laser performance is limited by the formation of molecular iodine. The formation of molecular iodine in the excited state (I*2) reduces the number of iodine atoms available to form IF*. In the ground state, molecular iodine (I2) absorbs the IF* laser emission at 485 and 491 nm.     

Gain studies of electron beam excited XeF laser mixtures

Detailed optical gain measurements of electron beam pumped Ar/Xe/NF3and Ne/Xe/NF3laser mixtures for theB rightarrow Xand theC rightarrow Atransitions of XeF at 351 and 488 nm are reported using a direct laser probe and two different fluorescence techniques.     

电子束的发散性对自由电子激光器输出性能的影响

研究表明,进入Wiggler场的相对论电子束的发散角增大,将降低自由电子激光器的增益,但小量的发散角可提高激光器的输出功率。最大容许的发散角由激光振荡条件决定。