利用受激布里渊散射改善偏振抽取腔光束质量的研究

在理论上分析了受激布里渊散射相位共轭效应和阈值效应对后向受激布里渊散射光束发散角的影响。在实验上，用受激布里渊散射相位共轭镜（SBS PCM）代替普通反射镜构成Nd:YAG激光器的偏振抽取腔，补偿了激活介质和光学元件造成的波前畸变，压缩了发散角，改善了光束质量。研究了抽运能量、透镜焦距等因素对受激布里渊散射偏振抽取腔输出光光束质量的影响。     

透镜焦距对受激布里渊散射光限幅特性的影响

采用受激布里渊散射(SBS)噪声起源理论模型，数值模拟了透镜焦距对SBS光限幅功率特性和能量特性的影响.结果表明，改变透镜焦距就可以方便的控制SBS光限幅的功率波形和输出能量.当采用焦距适中的透镜(f=15cm)时，可以得到较低的限幅输出能量；当采用短焦距的透镜(f=5cm)时，可以得到较理想的限幅功率波形.在实验上将波长1064nm、脉宽8ns、能量16mJ的Nd:YAG激光脉冲聚焦到CCl₄介质中，研究了限幅功率波形和限幅输出能量随透镜焦距的变化规律，实验结果与理论模拟相符合. 关键词： 受激布里渊散射 光限幅 数值模拟     

KrF激光受激布里渊散射反射率稳定性的研究

实验研究发现抽运功率密度（或抽运能量）的波动引起的受激布里渊散射(SBS)反射率的不稳定程度受实验参数（抽运能量、介质气压和透镜焦距）的影响.当抽运能量、介质气压和透镜焦距这三个参数同时满足下列条件时可以获得稳定的输出：抽运能量超过5倍的SBS阈值，介质气压在16×105Pa和透镜焦距在15—50cm的范围内；同时还发现当改变实验参数时SBS反射率与稳定性的变化规律完全一致，反射率越高稳定性越好.通过理论分析得到 SBS反射率的相对稳定度实际上是受GIL因子的影响，理论计算与实验符合得很好. 关键词： KrF激光 受激布里渊散射 反射率 稳定度     

鉴别CS2介质受激喇曼散射和受激布里渊散射阈值的微小差异的实…

本文提出一个测试ＣＳ２介质受激喇曼散射和受激布里渊散射阈值的微小差异的实验方法，并成功地获得阈值稍低的受激喇曼散射，而抑制了受激布里渊散射。     

宽带KrF激光抽运的受激布里渊散射反射率研究

实验上研究了宽带KrF激光抽运的受激布里渊散射(SBS)随抽运功率密度、介质气压和透镜焦距这三个实验参数的变化规律.在较低的抽运功率密度情况下，SBS反射率随抽运功率密度呈非线性增长；当抽运功率密度提高到一定程度，SBS反射率接近饱和；当功率密度继续增大，SBS 反射率随之下降.介质气压提高能够促进SBS的转换.透镜焦距长度的变化使SBS饱和反射率存在一峰值.理论上建立了宽带多模SBS模型，数值模拟结果与实验结果符合得很好，解释了宽带SBS反射率对实验参数的变化规律. 关键词： 宽带 KrF激光 受激布里渊散射(SBS) 反射率     

水体参量对受激布里渊散射阈值及增益的影响

针对水中受激布里渊散射阈值和增益这两个重要特征参量,理论分析了温度和盐度对水中受激布里渊散射增益的影响,同时采用耦合波方程与平均衰减系数相结合的方法,研究了阈值与温度和衰减系数的相关性。研究结果表明,受激布里渊散射的增益与温度和盐度正相关,随着温度和盐度的升高,受激布里渊散射增益增大;而受激布里渊散射阈值随着温度的增加而减小,随着衰减系数的增大而增大。研究结果对了解水中的受激布里渊散射过程提供理论依据。     

水体参数对受激布里渊散射阈值及增益的影响

受激布里渊散射在激光雷达海洋遥感领域具有广泛应用,而水体参数变化对其阈值及增益等关键特征参数影响的研究还很缺乏.本文利用分布式噪声模型及耦合波方程,理论分析了水的温度、压强和衰减系数对受激布里渊散射阈值和增益系数的影响.在理论分析基础上,设计了一种温度压强可控实验系统,采用平均衰减系数法实验测量了不同温度、压强及衰减系数下的阈值和增益系数.结果表明,受激布里渊散射阈值随压力和衰减系数的增大而增大,随温度的升高而减小,而增益系数则呈现与阈值相反的变化趋势.温度和衰减系数对阈值和增益系数的影响大于压力.研究结果对受激布里渊散射激光雷达海洋遥感探测具有重要意义.     

KrF激光在SF_6气体中受激布里渊散射的研究

用线宽０．５ｃｍ￣（－１）、脉宽２３ｎｓ的ＫｒＦ激光（２４８ｎｍ）在低气压ＳＦ＿６气体中进行受激布里渊散射（ＳＢＳ）的实验研究。测量了ＳＢＳ反射率随泵浦光能量、气体气压、透镜焦距等实验条件的变化关系，分析和讨论了气体气压、透镜瑞利范围对ＳＢＳ阈值的影响。     

水中受激布里渊散射阈值的研究

在对水中受激布里渊散射阈值的研究中,针对传统定义上的不足,提出一种新的定义和新的测量方法.测量了不同能量的光束在不同长度的水介质中传输,在宽线宽和窄线宽情况下水的衰减系数.通过水的衰减系数的变化来确定不同情况下受激布里渊散射的阈值.试验发现,水中的受激布里渊阈值在理想稳态和理想瞬态下是一个常数,只与泵浦激光和介质属性有关,和介质长度无关;在中间情况下,受激布里渊阈值是否与介质长度有关,还要根据具体情况来分析.     

受激布里渊散射光束发散性的研究

利用耦合波方程分析了相位共轭效应和受激散射阈值效应对受激散射光发散角的影响.在甲醇、乙醇和丙酮的受激布里渊散射实验中,分别获得受激布里渊散射光发散角减小3.2、3.0和2.4倍,脉宽压缩4.3、4.3和2.6倍,并获得散射光束发散角随泵浦能量的变化关系.     

Chaotic stimulated Brillouin scattering near the threshold in a fiber

We investigate the nonlinear dynamic behavior of stimulated Brillouin scattering (SBS) near threshold in the absence of feedback. When a cw Nd:YAG laser is injected into a single-mode optical fiber, the SBS signal exhibits intermittently appearing irregular self-pulsations near the threshold. By examining the time series of the SBS signals, we verify that the irregular SBS signal is one of the chaotic phenomena appearing near the bifurcation point.     

Theoretical investigation on the threshold value of stimulated Brillouin scattering in terms of laser intensity

The threshold value of stimulated Brillouin scattering (SBS) was investigated theoretically basing on a new concept of real gain length (RGL). It shows that for ideal steady-state SBS or ideal transient SBS, the threshold values are both constants and the later is five orders of magnitude larger than the former. Under general conditions, whether steady-state SBS or transient SBS will occur is determined by RGL. The SBS occurred in a long material may not be steady-state SBS.     

Experimental and theoretical study of self-phase modulation in sbs compression of high-power laser pulses

We study experimentally the behavior of the spectrum shape and Stokes frequency shift of stimulated Brillouin scattering (SRS)-compressed radiation within a broad range of incident-laser-pulse intensities from the threshold up to eight times the threshold values. We show that, at pulse compression of reflected radiation to subnanosecond durations (smaller than inverse spontaneous line widths), its spectrum monotonously shifts with increase in the exciting light intensity such that its Stokes shift decreases. At intensities increasing four times the threshold, the spectrum splits and acquires a twohumped shape, which is explained by the phase modulation near the SBS resonance. We construct an analytical model of self-phase modulation in SBS compression, describing the spectral splitting and chirping formation.     

Temperature dependence of threshold and gain coefficient of stimulated Brillouin scattering in water

Temperature dependence of threshold and gain coefficient of stimulated Brillouin scattering (SBS) was investigated. It was found that the threshold of SBS decreases with the increase of temperature. Based on the definition of the threshold, a new method was proposed for determining the gain coefficient of SBS of the material experimentally by measuring the threshold. It reveals that the threshold and the gain coefficient of SBS of a material are strongly related to temperature.     

Measurement of stimulated Brillouin scattering （SBS） threshold based on waveform variation of SBS optical limiting

This paper proposes a method for measuring the stimulated Brillouin scattering (SBS) threshold based on waveform variation of SBS optical limiting. The output waveforms for different pump power densities are numerically simulated, and validated in the Nd:YAG seed-injected laser system. The results indicate that SBS does not take place in the case of a low pump power density and thus the output power scales up linearly with pump power. Once the pump power density exceeds the SBS threshold, SBS takes place and thereby the energies are transferred from pump to Stokes. As a result, a small shoulder appears in the trailing edge of the output waveform, which provides another method to determine the SBS threshold.     

Improved output energy characteristic of optical limiting based on double stimulated Brillouin scattering

In order to improve the optical limiting performance based on stimulated Brillouin scattering (SBS), a method based on double SBS is proposed in this paper. The dependence of the output energy of optical limiting based on double SBS on the pump energy is numerically simulated, and experimentally validated with an Nd:YAG seed-injected laser. The results indicate that only the first SBS optical limiting works in the case of low pump energy. However, as the pump energy increases, the second SBS process can be activated if the transmitted power of the first SBS is still above the SBS threshold. Therefore, the output energy characteristic of optical limiting based on double SBS is much better than that based on single SBS. Owing to the sub-nanosecond response time and a high power threshold, the SBS optical limiting can provide protection in high power laser systems.     

相位调制信号对窄线宽光纤放大器线宽特性和受激布里渊散射阈值的影响

高功率窄线宽光纤放大器的输出功率主要受限于受激布里渊散射(SBS)效应,通过相位调制进行线宽展宽可以有效抑制SBS效应.基于窄线宽光纤放大器中的SBS动力学模型,研究了正弦信号、白噪声信号和伪随机编码信号(PRBS)对窄线宽光纤放大器光谱特性与SBS阈值的影响.研究发现,采用不同信号进行相位调制时,调制频率和调制深度等参数对调制后激光光谱的谱线间隔、谱线数目与光谱平整度的影响存在较大差异,进而影响放大器的线宽特性和SBS阈值.通过对比分析,给出了调制信号的类型选择和参数优化原则,能够为窄线宽光纤放大器的相位调制系统设计提供参考.     

Stimulated Brillouin scattering of Q-switched laser pulses in large-core optical fibres

Q-switched Nd : glass laser pulses of 60 ns duration are transmitted through multimode fused-silica fibres of 0.4–1 mm core diam and lengths of up to 20 m. For laser radiation with narrow spectral width, stimulated Brillouin scattering (SBS) is observed for energies well below the threshold energy of fibre damage. The SBS threshold is shifted beyond the threshold of fibre damage through increasing the spectral width of the laser radiation. The SBS threshold energies of step-index and gradient-index fibres are measured for various fibre and laser parameters.