序列脉冲倍频YAG激光器泵浦的氧气受激拉曼散射研究

对序列脉冲倍频ＹＡＧ激光器泵浦的氧气受激拉曼散射进行了研究。对氧气的受激拉曼散射池的热传导过程进行了数值模拟计算，实验研究了序列脉冲倍频ＹＡＧ激光器泵浦情况下氧气受激拉曼散射的热效应问题。     

大口径DKDP晶体受激拉曼散射增益系数的测量（英）

大口径KDP/DKDP晶体在强紫外光辐照下产生横向受激拉曼散射效应（TSRS）, 受激放大的拉曼散射光将导致激光能量损失甚至激光损伤, 测量DKDP晶体TSRS增益系数对设置激光装置的运行区间以确保晶体的安全使用非常重要。采用高精度光谱仪探测大口径DKDP晶体（氘含量65%）在351 nm激光辐照下的横向拉曼散射信号, 得到了拉曼散射光的增长曲线, 拟合得到的拉曼增益系数为0.109 cm/GW。同时, 实验结果表明晶体体损伤不影响TSRS增长行为, 表明晶体体损伤对拉曼增益系数测量结果的影响可以忽略。     

大口径DKDP晶体受激拉曼散射增益系数的测量（英文）

大口径KDP/DKDP晶体在强紫外光辐照下产生横向受激拉曼散射效应(TSRS),受激放大的拉曼散射光将导致激光能量损失甚至激光损伤,测量DKDP晶体TSRS增益系数对设置激光装置的运行区间以确保晶体的安全使用非常重要。采用高精度光谱仪探测大口径DKDP晶体(氘含量65%)在351nm激光辐照下的横向拉曼散射信号,得到了拉曼散射光的增长曲线,拟合得到的拉曼增益系数为0.109cm/GW。同时,实验结果表明晶体体损伤不影响TSRS增长行为,表明晶体体损伤对拉曼增益系数测量结果的影响可以忽略。     

D2受激拉曼散射产生的紫外激光用于O3差分吸收激光雷达的研究

脉冲Nd∶YAG四倍频激光(266nm)泵浦D2的受激拉曼散射第二级斯托克斯光(316.39nm)用作O3差分吸收激光雷达的λoff。为研究D2的受激拉曼散射效应和定量解释其物理机制作了一系列的实验。通过调节泵浦能量和气体压强,得到了各级散射光的能量转换效率,找到了第二级斯托克斯光的优化条件。     

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。     

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。     

时间位相调制对高强度三次谐波转换的影响

在惯性约束聚变研究中,为了利用光谱色散进行光束匀滑以及抑制KDP晶体等大口径光学元件中的横向受激布里渊散射,通常需要对激光脉冲进行时间位相调制.详细讨论了高功率条件下KDP晶体Ⅰ/Ⅱ角度失谐三倍频方案中,时间位相调制对三次谐波转换效率和脉冲频谱的影响.研究结果表明,时间位相调制会导致三次谐波转换效率明显下降.     

YbVO4晶体的受激拉曼散射

采用腔外单次通过方式,研究了一种新型晶体YbVO₄的受激拉曼散射.当抽运激光为532 nm皮秒脉冲时获得了3级斯托克斯线(558.47 nm, 587.92 nm, 620.67 nm)和1级反斯托克斯线(507.58 nm),测得YbVO₄晶体1级斯托克斯受激拉曼散射的稳态增益系数为17.8±0.2 cm/GW,受激拉曼散射的整体转换效率达到37%.实现了YbVO₄晶体对355 nm皮秒激光的受激拉曼散射,观察到1级斯托克斯线(366.1 关键词： 受激拉曼散射 稳态增益系数 转换效率 4晶体')" href="#">YbVO₄晶体     

YVO4晶体的高效受激拉曼散射

报道了YVO4晶体在532 nm、30 ps脉冲下的的高效受激拉曼散射。采用腔外单次通过方式测量了不同长度YVO4晶体1阶斯托克斯受激拉曼散射的阈值,并得到该晶体的稳态增益系数为16.0±0.5 cm/GW。实验中观察到2阶斯托克斯线(558.6 nm5、87.8 nm)和1阶反斯托克斯线(508.0 nm),受激拉曼散射的整体转换效率高于50%。     

水中受激拉曼散射的能量增强及受激布里渊散射的光学抑制

为提高液体介质中受激拉曼散射的输出能量,提出了通过温度调控来抑制受激布里渊散射的方法,设计了532 nm多纵模宽带脉冲激光泵浦的受激拉曼散射发生系统,测量了不同温度下水中前向受激拉曼散射及后向受激布里渊散射的输出能量,分析了水温、泵浦激光线宽及热散焦效应对受激拉曼散射输出能量影响的物理机制.实验结果表明:通过降低水温可实现对受激布里渊散射过程的有效抑制,同时减小热散焦效应带来的光束畸变,从而有效提高受激拉曼散射的输出能量.研究结果对液体介质中的受激拉曼散射多波长转换具有重要意义.     

Enhanced compression of femtosecond pulse in hollow-core photonic bandgap fibers

Compression of chirped free femtosecond pulses in hollow-core photonic bandgap fibers is investigated numerically. The results show that intrapulse stimulated Raman scattering can improve the quality of the compressed pulse. Positive third-order dispersion is the main limitation on the compression of the femtosecond pulse. However, the combined effect of the intrapulse stimulated Raman scattering and the negative third-order dispersion can form still shorter pulses than is possible with intrapulse stimulated Raman scattering alone. We also investigate the influence of width and peak power of input pulse on pulse compression.     

Frequency shifts in stimulated Raman scattering

The nonresonant contributions to the nonlinear susceptibility χ⁽³⁾ produce a frequency chirp during stimulated Raman scattering. In the case of transient stimulated Raman scattering, the spectrum of the generated Stokes pulse is found at higher frequencies than expected from spontaneous Raman data. The frequency difference can be calculated from the theory of stimulated Raman scattering.     

Fundamental Studies of Stimulated Raman Scattering and Adaptive Optics on the Basis of Stimulated Light Scattering

Some results associated with the fundamental investigations of stimulated scattering of light in various media are reported. A number of problems of adaptive optics based on stimulated scattering is studied. Concrete results of experimental investigations of physically important characteristics of conventional (spontaneous) and stimulated Raman scattering are presented and discussed. Among them are the scattering indicatrix and the relations between the phases of laser radiation incident on a substance and stimulated scattering. These results were first obtained in the G. S. Landsberg Optical Department of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences. Data on excitation sources and the radiation detection technique are systematized. The main characteristics of spontaneous Raman scattering and forward and backward stimulated Raman scattering (energy parameters, pulse duration, pulse shape, divergence, brightness, spectral width, far- and near-field intensity distributions) are presented. The results on dynamic holography, phase conjugation of light in stimulated scattering, and reconstruction and recording of information (images) with the help of amplifying dynamic holograms are presented. The physical mechanisms responsible for the interference field recording and the phase conjugation of pump radiation in stimulated light scattering are discussed. The data on phase conjugation for stimulated scattering excited by picosecond optical pulses and the results associated with the effect of excitation geometry on the optical phase conjugation in the case of stimulated scattering excited by nanosecond pulses are presented.     

Theoretical Treatment of Nonstationary Scattering by Phonons and Polaritons Part II. Transient Raman Scattering by Polaritons and Dipole Active Phonons

The stimulated Raman scattering by polaritons and phonons generated by the fluctuations of the crystal vibrations is investigated for the transient regime. The transient gain and the scattering energy is given for the case of retarded or advanced Stokes and polariton pulses in relation to the laser pulse. Moreover, the influence of phase modulation of the laser pulse on the transient SRS by polaritons is discussed.     

Stimulated Raman scattering pulses. I. Weak scattering

Rate equations are used to compute a weak stimulated Raman scattering pulse in the case where the scattered radiation energy can be neglected in the over-all energy balance. Expressions for the shape, position and height of the maximum, duration, and spectral width of the scattering pulse as functions of the parameters of the driving laser, scattering material, and observation conditions are derived.     

Double line stimulated Raman scattering in benzene

Simultaneous stimulated Raman scattering at the 992 cm^–1 and the 3063 cm^–1 line of benzene is observed by mode-locked ruby laser pulse excitation. The double line stimulated Raman scattering is initiated by self-focusing. The influence of small-scale self-focusing, self-phase modulation, and cross-phase modulation on the double line stimulated Raman scattering is discussed. At low pump pulse intensities, before the onset of small-scale self-focusing, the steady-state Raman gain factors of both Raman lines are determined by Raman energy conversion efficiency measurements.     

Superradiance and Raman scattering in three-level molecular system

A model is presented for the dynamics of superradiance, coherent and stimulated Raman scattering from an optically pumped three-level system. The evolution of the pumping and two counterpropagating waves in the adjacent transition are taken into account. The results of computer simulation show that by specifying the pumping pulse area, and active medium length and pressure we can control the parameters of the pulses in the adjacent transition. The possibilities of observing coherent Raman scattering dynamics, which are significantly different from that for stimulated Raman scattering, are shown. The results of simulation show that for the ultrashort pumping pulse the superradiative emission in the backward direction is formed within the coherence length near the entrance plane of the active medium.     

Input Power Conditions for Distributed Fiber Optic Temperature Sensors in Raman Optical Time-Domain Reflectometry

The critical power of the input pulse in which spontaneous Raman scattering is not seriously disturbed by stimulated Raman scattering in a fiber optic temperature sensor has been investigated experimentally and theoretically. The critical power determines the critical distance, which is nearly equal to the distance where optical time-domain reflectometry (OTDR) signal of the stimulated Raman scattering becomes maximum. From this fact, a new method to determine the critical input power with the OTDR system has been proposed, which may be applicable to most distributed fiber optic temperature sensors. It has been determined that the critical power of the input pulse is 4 watts for an infinitely long silica fiber.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.