受激布里渊散射介质CCl_4中脉冲传输与功率限幅特性

分析了受激布里渊散射介质CCl4 对纳秒激光脉冲的传输特性及功率限幅特性 .结果表明 :透射脉冲波形随抽运光能量增加而压缩变形 ,脉冲前沿保持高斯型 ,后沿被压缩成功率“平台” ,功率“平台”随抽运脉冲能量增加而逐渐变宽 ,但功率水平不变 ,表明该光学系统具有的功率限幅特性 .详细分析了功率限幅特性随抽运能量的变化规律和时间响应特性规律 ,采用脉宽为 10ns、波长为 1 0 6 μm的Nd :YAG激光脉冲进行实验验证 ,理论与实验结论相符合 .     

受激布里渊散射光限幅输出波形控制研究

数值模拟了种子场诱导受激布里渊散射光限幅过程的限幅输出波形特性.得到利用种子场控制限幅脉冲波形的规律：选取种子场脉冲宽度为抽运脉冲宽度的五倍，抽运脉冲相对于种子脉冲的延迟时间控制在与抽运脉冲宽度相当时，限幅输出波形最佳.限幅输出波形同时受抽运光功率影响，随抽运能量的增加，限幅脉冲功率不断下降，直至趋于0. 关键词： 受激布里渊散射 限幅输出波形 注入种子     

抽运能量对受激布里渊散射光限幅特性的影响

采用布里渊噪声起源模型,数值模拟了受激布里渊散射介质CCl4对波长1064nm的Nd：YAG纳秒激光脉冲的传输特性及光限幅特性。入射抽运脉冲能量较低时,非线性介质对纳秒激光脉冲呈光学透明。入射抽运脉冲能量高于受激布里渊散射产生阈值后,透射脉冲峰值受限,脉宽压缩,能量趋于饱和,说明该光学系统同时具有光功率限幅和能量限幅的光限幅特性。利用理论模型模拟了如下光限幅参量：透射脉冲峰值功率、透射能量、能量透射率、脉宽压缩率依赖抽运光能量的变化关系。相应的理论模拟计算结果由实验进行验证,实验结果与理论模拟相符合。     

水中受激布里渊散射脉冲的反常压缩

受激布里渊散射(SBS)具有脉冲压缩的特性,受激布里渊散射的脉冲宽度随着抽运能量的增大而变小,在水中可以达到几百皮秒的量级.本文在实验上观察到一种受激布里渊散射的脉冲宽度随抽运能量增大而变大的现象,这里称之为反常压缩.SBS的脉冲反常压缩和脉冲压缩与抽运光的强弱会聚情况有关.利用数值模拟,模拟了强弱会聚情况下抽运光在水中的传输规律,强弱会聚情况的抽运光对受激布里渊散射形成的有效增益长度不同:抽运光强会聚时有效增益长度短,形成SBS脉冲宽度的反常压缩;弱会聚时有效增益长度长,也就是正常的SBS脉冲压缩.     

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     

利用染料片吸收控制受激布里渊散射功率限幅波形

理论研究了受激布里渊散射过程中功率限幅响应特性.采用高斯型入射脉冲，数值模拟了抽运参数(抽运峰值功率密度、抽运脉冲宽度)，介质参数(增益系数、声子寿命)和结构参数(聚焦透镜焦距、介质池长)等物理参数影响限幅输出波形中剩余峰的特性规律.对如何控制剩余峰进行了理论分析.研究表明，声子寿命较小、增益系数大的布里渊介质光限幅响应较好，声子寿命较大、增益系数小的布里渊介质光限幅响应较差；无法单纯通过控制布里渊介质参数来完全消除剩余峰.实验上采用染料片吸收剩余峰，获得接近平顶的限幅输出波形.     

非线性光纤环镜在受激布里渊散射慢光级联系统中的可行性研究

基于非线性光纤环镜(NOLM)的脉冲压缩特性,分析了NOLM在基于受激布里渊散射(SBS)慢光级联系统中对延迟脉冲的影响.利用环形结构来模拟多次级联,有效地降低了系统的复杂度,得到了在不同抽运光功率和级联次数下脉冲的延迟输出特性.理论分析表明,NOLM可以有效地抑制SBS慢光级联系统中延迟脉冲的展宽,抽运光功率决定了展宽因子的变化趋势及最终稳定值的大小,展宽因子在级联4次时趋于稳定值,恰当选取抽运光功率可实现脉冲的零展宽延迟;改变抽运光功率和级联次数可以实现延迟量的连续可调,且延迟量理论上不受限制;增大抽 关键词： 慢光 脉冲压缩 非线性光纤环镜 受激布里渊散射     

受激布里渊散射对纳秒激光脉冲光限幅规律

 研究了受激布里渊散射对纳秒激光脉冲的光限幅效应。针对四氯化碳介质研究了受激布里渊散射对2ns激光脉冲的光限幅和稳定输出能量的特性,给出了光限幅特性及输出能量与光限幅介质的结构参数之间的关系。对于输入能量波动范围在 13%的激光脉冲,实验获得输出能量波动范围为 7%,与理论分析的结果基本符合。     

三倍频Nd:YAG激光抽运氧气中的受激拉曼和布里渊散射

报道了三倍频脉冲Nd：YAG激光（355nm）在两种不同带宽模式下抽运氧气中受激拉曼散射（SRS）和受激布里渊散射（SBS）的实验研究。在宽带（约1cm^-1）抽运模式下,只测到了前向受激拉曼散射,而没有观察到后向散射,其一级和二级斯托克斯最大能量转换效率可达22％和8％。在窄带（约0．003cm^-1）模式下,前向、后向受激拉曼散射和受激布里渊散射都测量到了,但大部分抽运能量都转换到受激布里渊散射,其转换效率可达67％。测量了两种带宽模式下各散射组分在它们最佳转换时的波形;窄带情况下后向受激拉曼散射和受激布里渊散射的脉宽分别可压窄至1．5ns和2．3ns,不到抽运脉宽的三分之一,使得受激布里渊散射峰值功率可大大高于抽运功率。对氧气中前向、后向受激拉曼散射和受激布里渊散射之间的竞争进行了讨论。     

三倍频Nd∶YAG激光抽运氧气中的受激拉曼和布里渊散射

报道了三倍频脉冲Nd∶YAG激光(355 nm)在两种不同带宽模式下抽运氧气中受激拉曼散射(SRS)和受激布里渊散射(SBS)的实验研究。在宽带(约1 cm-1)抽运模式下,只测到了前向受激拉曼散射,而没有观察到后向散射,其一级和二级斯托克斯最大能量转换效率可达22%和8%。在窄带(约0.003 cm-1)模式下,前向、后向受激拉曼散射和受激布里渊散射都测量到了,但大部分抽运能量都转换到受激布里渊散射,其转换效率可达67%。测量了两种带宽模式下各散射组分在它们最佳转换时的波形;窄带情况下后向受激拉曼散射和受激布里渊散射的脉宽分别可压窄至1.5 ns和2.3 ns,不到抽运脉宽的三分之一,使得受激布里渊散射峰值功率可大大高于抽运功率。对氧气中前向、后向受激拉曼散射和受激布里渊散射之间的竞争进行了讨论。     

Optical limiting effect based on stimulated Brillouin scattering in CCl4

The optical limiting effect based on stimulated Brillouin scattering (SBS) in a nonlinear medium was investigated. We numerically treated the nonlinear propagation process with a theoretical model, which includes the spontaneous nature of the initiation of SBS, and obtained optical limiting effect in the process. Energy limiting, pulse reshaping and stabilization have been demonstrated on SBS mechanism with the nonlinear medium CCl_4. The input optical signals were Nd:YAG nanosecond laser pulses with width varying from 16ns to 7ns then to 2ns, the relationship between the transmitted signal and launched pump signal was shown. In the experimental regime, the most stable pulse and a superior energy stabilization of the transmitted pulse were obtained when the laser pulse-width became as short as 2ns. For the energy variation of laser pulses in a wide range of 14－88mJ, the output energy was limited in a quite narrow range 4.5－5.5mJ.     

A new method for measuring the threshold of stimulated Brillouin scattering

A new method for measuring the threshold of stimulated Brillouin scattering (SBS) based on the generation location of a Stokes beam is proposed for the first time to our knowledge. The length of the medium cell is selected to be longer than the free gain length of pump pulses in the Brillouin medium. The reflected light from a certain mirror in front of the medium cell is chosen as the reference beam, and the SBS threshold is measured by the "jump" of the delay between the Stokes beam and the reference beam. An 8-ns Q-switched single-longitudinal-mode pulse is used as the pump and the typical SBS medium FC-72 is selected as the nonlinear medium in our experiment. The SBS threshold intensity is measured to be 173-178 mW/cm 2 , which is consistent with existing results measured with the transmitted energy limiting method.     

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.     

Dynamics of the Stokes pulse in a Brillouin amplifier

We show that the output Stoke pulse from a continuously (CW) pumped stimulated Brillouin scattering (SBS) amplifier is the sum of the transmitted input Stokes pulse, which propagates undistorted through the medium without amplification and additional delay, and of a Stokes shifted pump signal reflected by the electrostrictively induced acoustic wave, which contributes to the Stokes output signal with a delay determined by the time required for build up of the acoustic wave.