Influences of finite gain bandwidth on pulse propagation in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulations with the nonlinear Schr¨odinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing a small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful for the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

Influences of finite gain bandwidth on pulse propagating in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulating with the nonlinear Schrödinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful to the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

拉曼效应和参量放大共同作用下增益谱特性

根据激光脉冲在双折射光纤中传输时, 拉曼效应和参量放大共同作用下所所遵循的耦合模方程, 基于平行拉曼增益的洛伦兹模型, 给出了输入抽运波偏振方向沿相互正交的双折射轴时, 拉曼效应和参量放大共同作用所导致的增益. 讨论并分析了在不同色散区相关参量对增益谱特性的影响. 结果表明, 拉曼效应改变了非线性和色散的相互平衡, 使得参量放大斯托克斯波与反斯托克斯波增益谱彼此不对称; 当输入功率一定时, 其增益谱结构确定, 非线性系数和色散系数两者之间相对变化时, 增益谱的强度和展宽有所改变.     

Frequency domain aperture for the gain bandwidth reduction of stimulated Brillouin scattering

In this Letter, we propose a novel method based on the inhomogeneous Brillouin gain saturation to reduce the gain bandwidth significantly below its natural value. Based on our first experiments, we report a decrease of the bandwidth in a standard single mode fiber down to 3 MHz.     

Delay-dependent amplification of a probe pulse via stimulated Rayleigh scattering

Stimulated Rayleigh scattering of pump and probe light pulses of close carrier frequencies is considered. A nonzero time delay between the two pulses is shown to give rise to amplification of the delayed (probe) pulse accompanied by attenuation of the pump, both on resonance and off resonance. In either case, phase-matching effects are shown to provide a sufficiently large gain, which can exceed significantly direct one-photon absorption losses.     

用激光增益获取弱增益拉曼模式的受激拉曼散射光谱

当酒精的弱增益拉曼模式处于罗丹明640染料分子的激光增益范围时，在由悬垂液滴构成的圆形谐振腔中，观察到乙醇分子C—H伸缩系列模中多个弱增益拉曼模式的受激拉曼散射（SRS）光谱.随着抽运光的增强，迅速增长的强增益拉曼模式的受激辐射抑制了其他弱增益模式的SRS，并导致染料激光的完全淬灭.通过分析圆形腔腔模的光子速率方程和激光染料分子的三能级粒子数速率方程，解释了观察到的实验现象. 关键词： 受激拉曼散射 悬垂液滴 弱拉曼增益模式 激光增益     

Subfemtosecond pulse generation and multiplicative increase of pulse spacing in high-order stimulated Raman scattering

We demonstrate a technique for multiplicatively increasing the pulse spacing of subfemtosecond pulse trains generated by high-order stimulated Raman scattering, which uses pairs of off-resonant two-photon excitation of a molecular Raman mode to establish strong molecular modulation in the medium. Every laser pair has two single-mode laser beams tuned slightly off two-photon resonance, and the laser pairs have their corresponding carrier frequencies shifted from each other by one half, one third, or one fourth of the selected molecular Raman mode frequency. Theoretical analyses and calculations based on the fundamental vibrational transition of solid hydrogen show that the pulse spacing of the subfemtosecond pulse trains thus generated can readily be doubled, tripled, or even quadrupled.     

皮秒激光瞬态受激喇曼散射的实验研究

本文采用对撞脉冲锁模Nd:YAG激光器输出10ps脉冲串,经KTP非线性晶体腔外倍频,泵浦喇曼介质为二甲亚砜(DMSO)液体.实验研究了不同透镜焦长、焦点位置及不同喇曼介质氏度对瞬态受激喇曼散射的影响,获得了能量转换效率分别为45.6%和10.5%的前、后向一阶斯托克斯-喇曼散射光,并对实验结果进行了讨论.     

Raman amplification and optical short pulse generation in a waveguide with periodic gain

In this paper a new configuration of amplification is proposed for Raman amplification. In this new configuration a spatial periodic Raman gain is used to amplify a CW Raman seed that generates a short optical pulse taking into account the SPM, XPM, walk-off and pulse depletion. The amplification process is accomplished by using an intense pump pulse where its energy is transferred through SRS effect. A CW weak seed is used to represent the signal to be amplified and for pump is used a Gaussian pulse. We discuss the advantages to this configuration. First, this scheme means that the Raman-gain coefficient assumes a periodic characteristic and like a modulation process, it gives possibility to control the energy transfer from the pump to Raman seed. Second, the efficient use of the parameters of the periodic Raman coefficient function, like amplitude and frequency of the modulation, can result in a more efficient control of the signal amplification. This new configuration provides some very interesting features in the Raman amplification process when compared to the standard procedure. A complete discussion of this configuration is presented.     

ICF驱动器长脉冲下三倍频晶体中的横向受激拉曼散射

ICF驱动器在脉宽为3ns的长脉冲条件下运行时,三倍频晶体中的横向受激拉曼散射效应将比短脉冲条件下的效应更为显著。针对长脉冲运行时,KDP晶体和KD*P晶体产生的横向受激拉曼散射光对晶体的危害性作了对比分析,并研究了横向受激拉曼散射效应与增益系数之间的关系,为选择何种晶体作为三倍频晶体提供了理论依据。     

Time-domain pulse property of stimulated Raman scattering in a multimode optical fiber

The time-domain pulse property of quasi-steady stimulated Raman scattering (SRS) in a multimode optical fiber, pumped by an A-O Q-switched Nd: YAG laser, is studied both experimentally and theoretically. Good agreement has been achieved between theory and experiment. Discussion shows that the variation of the Stokes pulse width (FWHM)t _s depends on the shape of input pump pulse.     

ICF驱动器长脉冲下三倍频晶体中的横向受激拉曼散射

 ICF驱动器在脉宽为3ns的长脉冲条件下运行时，三倍频晶体中的横向受激拉曼散射效应将比短脉冲条件下的效应更为显著。针对长脉冲运行时，KDP晶体和KD*P晶体产生的横向受激拉曼散射光对晶体的危害性作了对比分析，并研究了横向受激拉曼散射效应与增益系数之间的关系，为选择何种晶体作为三倍频晶体提供了理论依据。     

Applications of stimulated Raman scattering

The applications of stimulated Raman scattering reviewed in this paper include: determination of spontaneous Raman parameters and nonlinear susceptibilities by gain measurements and coherent anti-Stokes Raman spectroscopy, excitation of molecular vibrations and lattice waves and measurement of their relaxation times, generation of intense tunable light in the infrared region of the spectrum. The main results of the theory of stimulated Raman scattering relevant to the understanding of these applications are discussed.     

氘含量对DKDP晶体横向受激拉曼散射增益系数的影响

本文测量了不同氘含量K(H_1-xD_x)₂PO₄晶体(DKDP晶体)在Z(XX)Y散射配置下的自发拉曼散射光谱, 并详细分析了氘含量对与横向受激拉曼散射(TSRS)增益系数有关的拉曼频移、半峰宽和散射强度的影响. 然后通过与去离子水拉曼散射对比得出了不同氘含量DKDP晶体的TSRS增益系数. 结果表明随着氘含量的增加DKDP晶体的TSRS增益系数先减小至KDP晶体的40.1%, 后增大至68.9%; 本文认为掺氘后拉曼半峰宽的变化是引起TSRS增益系数随氘含量变化的主要原因.     

Studies of stimulated Raman scattering

The dependence of the excitation threshold and the intensity of the first Stokes component on the properties of the scattering material, the concentration of its molecules, and the exciting light intensity has been studied. It has been found that the intensity of stimulated Raman scattering lines depends exponentially on the intensity of the exciting light and the concentration of the scattering molecules. This dependence is in agreement with the theory developed.The author are gratful to P. A. Bazhuln, N. G. Basov, and A. M. Prokhorov for the present study.     

Stimulated Raman scattering for variable gain amplification of small optically carried microwave signals

Stimulated Raman amplification of optically carried microwave signals in optical fibers is experimentally investigated. In the backward configuration which is shown to be less noisy than the forward one, net amplification factors larger than 20 dB are demonstrated in the low signal regime with better relative intensity noise (RIN) values than using erbium-doped-fiber amplifiers. Due to the RIN flatness with respect to the gain of the stimulated Raman amplifier high quality variable gain amplification of optically carried microwave signals could be implemented using optimized Raman amplifiers.     

Influence of gas circulation on stimulated Raman scattering and amplification of ultrashort laser pulses in methane

Applying gas recirculation in a high pressure cell, laser pulses of 1 ps at 400 nm and with a repetition rate of 1 kHz were frequency shifted by stimulated Raman scattering and amplification in methane gas at high pressure. We studied the influence of gas recirculation on the conversion efficiencies into the Stokes and anti-Stokes components as well as on their spatial distributions and spectral shapes using generator and generator-amplifier arrangements. For high pump energies, recirculation in the generator cell decreases conversion efficiency into the first Stokes component whereas it increases conversion into higher Stokes and anti-Stokes components. It results in a significantly improved spatial characteristics of the frequency-shifted radiation, however, is accompanied by a substantial spectral broadening. Using gas recirculation in the generator-amplifier arrangement we achieved a conversion efficiency into the first Stokes component of about 50% with highly improved spatial and spectral characteristics.