动态主观散斑的时间相关性研究

根据散射屏移动时动态主观散斑时间相关公式,分析了成像系统主要参数对动态主观散斑时间相关性的影响：一般情况下屏表面参数对散斑的时间相关性影响较小;激光光斑大于成像系统物面分辨斑时,散斑的时间相关性由透镜孔径大小决定;激光光斑小于成像系统物面分辨斑的尺寸时,减小激光光斑尺寸能减弱散斑时间相关性。对于以上结果进行了相关的理论模拟和部分实验验证,通过模拟发现,激光光斑小于成像系统物面分辨斑时,散斑时间相关长度和光斑尺寸大小成正比。结论对于激光投影系统中利用时间平均进行的散斑抑制具有指导意义。     

双频塞曼He-Ne激光g1(τ)的时谱特性及其可能应用

本文从塞曼激光器典型的频谱结构出发,导出了双频塞曼He-Ne激光时间相干度g(1)(τ)在纵模频率漂移效应作用下的时谱公式,分析了相应的时谱特性和频率调谐特性,并在此基础上探讨了g(1)(τ)时谱特性在某些激光参数测量中的可能应用。     

阵列激光器主动锁相技术研究

为了获取高能量、高光束质量的激光输出,通过对激光的统计性质进行研究,提出了一种新型的阵列锁相技术,即利用一个控制系统,以外界介入的方式控制阵列激光的相位,对激光相位进行校正,减小或消除激光位相随机漂移,实现阵列激光独立单元间的位相锁定,保证良好的互相干特性.利用随机过程理论,详细分析了几种情况下激光的时间相干特性,根据各种情况下相干特性的比较结果得知,该锁相系统大大改善了激光之间的互相干特性.     

高斯-谢尔脉冲在单模光纤中的传输特性研究

为了研究高斯-谢尔模型(GSM)脉冲在单模光纤中的传输特性, 采用相干函数传播分析法推导出GSM脉冲经单模光纤传输后输出脉冲的时间相干函数解析表达式, 在此基础上分析脉冲宽度、相干时间和功率谱等特征量的变化, 并推导出在远端条件下单模光纤的时域广义范西特-泽尼克定理。结果表明, GSM脉冲在单模光纤中的传输存在功率谱和全局相干度两个守恒量, 且二者是一致的。该研究结果对激光传输领域具有一定的理论和现实意义。     

强THz场下半导体中动力学量子干涉的控制

半导体中载流子的量子相位相干性、退相干和多体关联效应之间的相互影响 ,以及量子干涉的可控性是当前半导体物理研究的一个关注焦点。作者最近提出半导体超快光学过程中的一种退相干机制 :激子动力学Fano共振。这种动力学量子干涉可以用 THz交流场强控制。利用激子动力学 Fano共振效应 ,在半导体材料吸收光谱与瞬态光谱中可以观测到强 THz场下的激子稳化效应 ,即激子电离率随 THz场强增加而下降的现象。以此可实验验证有争议的原子绝热稳化问题     

Coherent spontaneous emission and spontaneous phase locking in afree-electron laser

We present measurements that demonstrate the existence of spontaneous coherence between independently generated laser pulses in the FELIX free-electron laser. The experiments show that the interpulse coherence is caused by a high level of coherently enhanced spontaneous emission. We have been able to manipulate the level of interpulse coherence by changing the settings of the electron accelerating system. The shape of the electron bunches critically determines the amount of coherent emission. Results of simulations of the acceleration process are used to discuss the influence of the accelerator parameters on the electron bunch shape. The experimentally determined correlation function of the laser pulses is reproduced by a simple pulse-evolution model. Thereby, an estimate of the timing jitter of the RF accelerating system is obtained     

基于微型光机电系统扫描镜技术的激光散斑抑制方法

激光固有的时间和空间相干性,造成的散斑现象成为实现激光显示技术的瓶颈。针对激光显示的消散斑问题,提出了一种基于微型光机电系统(MOEMS)扫描镜技术的散斑抑制方法,并设计了一种简单的二维扫描镜结构,为开发非运动式、小体积、低功耗、高速低成本电调制的MOEMS,实现对激光散斑的抑制,标准化消相干器件的工艺的开发和规模化生产技术提供了参考。     

Coherence of a room-temperature CW GaAs/GaAlAs injection laser

The temporal coherence of a stripe-geometry double-heterojunction GaAs/GaAlAs laser operating CW at room temperature was determined. A heterodyne detection scheme was used involving the mixing of the laser field with a frequency-shifted and time-delayed image of itself in an interferometer. Because the laser device oscillated in several longitudinal modes, the autocorrelation function of its output exhibited resonances for specific time delays. The rate at which the amplitude of these resonances decreased with increasing time delays provided a measure of an apparent coherence length associated with individual longitudinal modes. The coherence length, so defined, was found to increase linearly with drive current in excess of threshold. This observation is interpreted as evidence that the intrinsic linewidth of a longitudinal mode is inversely proportional to the coherent optical power in that mode. Apparent coherence lengths were a few centimeters for a few milliwatts of total optical power emitted per facet. For a perfectly balanced interferometer, a sharp heterodyne beat signal was also observed when the laser device was operated considerably below threshold, i.e., in the LED mode.     

A synthesized method to improve coherence in semiconductor lasersby electrical feedback

A method for improving coherence in semiconductor lasers by negative electrical feedback is proposed for stabilization of the center frequency of the field spectrum, linewidth reduction of the field spectrum, frequency tracking to another highly coherent laser, and stable and wideband frequency sweep. Experimental center frequency stabilization of the master laser showed that the magnitude of frequency fluctuations was reduced to 50 kHz at the integration time τ=3 s. The linewidth of the master laser was reduced to 100 kHz, which was 1/50 that of the free running laser. Under these frequency control conditions, the frequency of the slave laser was controlled so that the phase of the heterodyne signal between the master and the slave lasers could be locked to that of a stable microwave synthesizer. The slave laser frequency tracked accurately to the master laser frequency     

An excimer-pumped β-BaB2O4 opticalparametric oscillator tunable from 354 nm to 2.370 μm

A pulsed singly resonant optical parametric oscillator (OPO) has been constructed which can provide tunable coherent radiation over the entire wavelength range extending from 354 nm in the near ultraviolet, throughout the visible, to 2.370 μm in the near infrared using a single β-BaB₂O₄ crystal. The oscillator is pumped at 308 nm by a pulsed narrow band injection-seeded XeCl excimer laser in a near-field pumping configuration, and energy conversion efficiencies (optical-to-optical) in excess of 10% have been obtained in a 12-nm-long crystal across the OPO tuning range. The requirements placed upon the spectral and spatial coherence of the pump laser for optimum OPO operation are discussed. Experimental results on several oscillator parameters, including tuning range, oscillation threshold, energy conversion efficiency, and spatial and temporal characteristics, are presented     

A review of stimulated Brillouin scattering excited with a broad-band pump laser

Stimulated Brillouin scattering (SBS) excited by a pump laser with a bandwidth large compared to the Brillouin linewidth is reviewed. SBS amplifier results show that either for low gain or for short pulses, the broad-band SBS gain is substantially lower than the steady-state gain. In the high gain limit, however, the fast phase fluctuations that are typical of a broad-band pump have a small effect on amplifier gain. Results for SBS that grows from noise show that fast pump phase fluctuations affect the gain only under two conditions. The first is when the coherence length of the pump is shorter than the gain length in the SBS medium. The second is when the pump is made up of two or more temporal modes separated by more than the SBS linewidth and aberrated with independent spatial profiles. In this case, the quality of wavefront inversion may be badly degraded as well. Areas for further work, including competing nonlinearities, are discussed.     

对通过光纤的激光时间相干性的实验研究

对通过光纤的激光时间相干性及其变化规律进行了实验研究,并提出一种确定时间相干函数的实验方法.     

Amplified spontaneous emission in narrow-band pulsed dye laser oscillators--Theory and experiment

We have investigated the effect of amplified spontaneous emission (ASE) on the spectral and temporal characteristics of narrow-band pulsed dye laser oscillators. The space and time dependent rate equations for the molecular populations and photon fluxes have been solved numerically to study the dependence of ASE on various laser parameters and the effects of ASE on the spectral and temporal profile of the dye laser output. To account for the diffraction losses present in a real dye laser oscillator, appropriate feedback factors for the laser and ASE photon fluxes were introduced into the boundary conditions for the oscillator. These theoretical results have been substantiated by experimental measurements of ASE in a narrow-band pulsed dye laser oscillator. We show that a considerable reduction of ASE in a grazing incidence grating dye laser oscillator can be obtained by appropriately shaping the pump pulse. Oscillations observed in the temporal output of pulsed dye lasers are also discussed.     

激光显示中散斑的抑制

文章首先概述了散斑的形成机理,接着简述了在近场条件下通过降低激光的时间或空 间相干性来抑制散斑的许多方法,并具体分析了仅通过降低激光的相干性来减弱激光显示中散斑的缺陷。提出一种在远场条件下减弱散斑的两维扫描复面转镜,且详细说明了该转镜的工作原理,当合成的激光束通过旋转的复面镜时,移动的干涉条纹在屏幕上产生“沸腾”的散斑图样。最后以红光为例,说明了合成光束通过转镜时显示屏幕上散斑对比度的降低,显示了二维转镜有效地抑制了激光显示中的散斑现象。     

Comparison of optical processing techniques for optical microwavesignal generation

Recently, there have been several proposals on using the higher RF harmonics of detected pulses from mode-locked semiconductor lasers as a source of microwave and millimeter waves. This paper compares the performance of three optical techniques of signal processing that have been proposed to select a higher harmonic of a mode-locked laser, by using extensive numerical simulations. We show that techniques using delays and splitters are insensitive to the coherence properties of the source, but can introduce amplitude patterning if pulses overlap when recombined. We see that techniques relying on optical filtering to select optical modes require extremely high-Q filters and, thus, are extremely sensitive to tuning. A Fabry-Perot interferometer (FPI) is the optimum fitter method in terms of power efficiency for low harmonics, but using two separate bandpass filters can give comparable efficiency when selecting higher harmonics. We also show that gain-switched lasers are unsuitable as sources when used with narrow-band optical filtering techniques because of their low pulse-to-pulse optical coherence     

C-band repeat-pass interferometric SAR observations of the forest

Properties of ERS-1 C-band repeat pass interferometric SAR information for a forested area are studied. The intensity information is rather limited but, including coherence and effective interferometric SAR (INSAR) height, more information about the forest parameters can be obtained via satellite. Such information is also important for correction of INSAR derived topographic maps. Coherence properties have been used to identify forested/nonforested areas and the interferometric effective height of the forest determined by comparison to a DEM of the area. The authors have developed a model to relate basic forest properties to INSAR observations. These show that the coherence and interferometric effective height of a forested area change between image pairs. The model demonstrates how these properties are related to the temporal decorrelation and the scattering from the vegetation canopy and the ground surface. Gaps in the vegetation are found to be important in the characterization of boreal forests     

脉冲和连续多色光源照明下光栅泰伯效应的等价性

利用部分相干光理论对多色光源照明下光栅的菲涅耳衍射进行了理论分析，得到了任意谱相干度照明下光栅衍射光强分布的一般公式，并对脉冲激光光源和连续的多色光源照明下光栅的菲涅耳衍射进行了相应的数值计算，进而讨论了光源的频谱分布对光栅泰伯效应的影响。理论结果表明超短脉冲的有限弛豫时间对光栅自成像的影响与多色连续光源的谱分布对光栅自成像的影响完全等价。这一等价性为借助于连续多色光照明下光栅的菲涅耳衍射来研究超短脉冲激光照明下光栅的菲涅耳衍射提供了理论依据。实验中选用发光二极管(LED)作为照明光源，对连续多色光照明下光栅的自成像分布进行了测量，实验结果和理论分析相符合。     

直接调制半导体激光的相干性

本文分析了直接调制半导体激光的相干性，并予实验证实。对深入了解直接调制半导体激光的特性，具有实用价值。     

四倍频Nd：YAG激光器制作光纤布喇格光栅

报道用四倍频Ｎｄ：ＹＡＧ激光器产生的２６６ｕｍ的光波．在高掺锗光纤中成功地写入了ＦＢＧ的实验结果。     

Vertical cavity surface-emitting semiconductor laser with CWinjection laser pumping

Room-temperature CW operation of a GaAs/AlGaAs vertical cavity surface-emitting laser with a resonant periodic gain medium, using a GaAs/AlGaAs diode laser array as a pump source, is discussed. Pumping thresholds as low as 11 mW at 730 nm, output powers as high as 10 mW at 856 nm, and external quantum efficiencies as high as 70% are obtained, with considerably improved temporal and spatial coherence properties compared to the pump laser. This is the first reported operation of such a laser with an efficient, compact pump source, demonstrating its suitability for efficient integration