一套高温高压原位拉曼散射、布里渊散射测量系统

本文描述了一套利用激光加热技术、金刚石对顶砧高压技术,集成共聚焦拉曼光谱测量、六通道布里渊散射光谱测量、以及黑体辐射光谱测温,成功搭建起来的高温高压原位拉曼散射、布里渊散射的光学测量系统。利用该系统,并结合薄膜沉积金属、光刻技术改进了金刚石对顶砧中样品的装填方法,解决了样品透明不易加热的问题。已利用该系统得到液态氩在0.85 GPa常温状态下和14.58 GPa熔融状态下的体声速分别为1.85 Km/s和5.19 Km/s。     

Coupled longitudinal and transverse stimulated Brillouin scattering in single-mode optical fibers

Due to their finite numerical aperture, both longitudinal and transverse stimulated Brillouin scattering can occur in single-mode fibers. We discuss the role of the fiber structure and propose a coherent model accounting for both effects. We show experimentally and numerically that, in some cases, the perturbative cladding Brillouin scattering (CBS) can severely affect the dynamics of SBS Brillouin fiber lasers. New dynamical regimes of long-fiber Brillouin ring lasers are presented, including stable trains of modulated pulses. Received 17 September 2001 / Received in final form 5 March 2002 Published online 28 June 2002     

基于激光布里渊散射的高速气流测试技术

激光布里渊散射是由介质密度涨落引起的一种非弹性散射现象,其散射谱特征参数（频移、线宽）取决于散射角和散射介质压强、温度等参数,通过探测高速气流激光布里渊散射谱,可反演获得高速气流压强、温度等参数。介绍了基于激光布里渊散射原理的高速气流参数测试原理,设计了一种基于法布里 珀罗干涉仪的高速气流参数测试装置,搭建实验平台获取了高速氮气气流的激光布里渊散射谱。实验结果表明,通过激光布里渊散射谱获得的高速气流压强、温度值与理论值相对误差在15%以内。     

1064nm红外激光大气布里渊频移量模型

1064nm激光常用于大气环境监测。以激光信号在传输介质中布里渊散射频移量模型为基础,依据相关大气数据建立1064nm激光大气中布里渊散射信号检测的大气探测模型。该模型将布里渊频移量归一为只与大气高度这一单参数相关的函数,详细地描述了0～1000km范围内大气布里渊频移量的连续分布状态。结果表明在0～1000km的海拔高度范围内,1064nm激光大气的布里渊散射频移量以非单调的形式分布在0.5～1.2GHz之间。     

Brillouin-Raman comb fiber laser with cooperative Rayleigh scattering in a linear cavity

We demonstrate a multiple-wavelength Brillouin comb laser with cooperative Rayleigh scattering that uses Raman amplification in dispersion-compensating fiber. The laser resonator is a linear cavity formed by reflector at each end of the dispersion-compensating fiber to improve the reflectivity of the Brillouin Stokes comb. Multiple Brillouin Stokes generation has been improved in terms of optical signal-to-noise ratio and power-level fluctuation between neighboring channels. Furthermore, the linewidth of the Brillouin Stokes is uniform within the laser output bandwidth.     

Enhancement of stimulated Brillouin scattering of higher-order acoustic modes in single-mode optical fiber

Solving the elastic wave equation exactly for a GeO2-doped silica fiber with a steplike distribution of the longitudinal and shear velocities and density, we have obtained the dispersion, attenuation, and fields of the leaky acoustic modes supported by the fiber. We have developed a model for stimulated Brillouin scattering of these modes in a pump-probe configuration and provided their Brillouin gains and frequencies for an extended range of core sizes and GeO2 doping. Parameter ranges close to cutoff of the acoustic modes and pump depletion enhance the ratio of higher-order peaks to the main peak in the Brillouin spectrum and are suitable for simultaneous strain-temperature sensing.     

Theoretical investigation on the pumping effect of stimulated Brillouin scattering on stimulated Raman scattering in water

The pumping effect of stimulated Brillouin scattering on stimulated Raman scattering is investigated theoretically through the coupled wave equations of stimulated Brillouin scattering and stimulated Raman scattering. The numerical simulations are in agreement with the experimental results. They indicate that the backward stimulated Raman scattering is excited and amplified collectively by both pump laser and stimulated Brillouin scattering.     

Brillouin lidar and related basic physics

The principle of a lidar based on Brillouin scattering is introduced. The basic physics of the Brillouin lidar is discussed. The applications of the Brillouin lidar in remote sensing of the ocean, such as measurement of the sound speed and the bulk viscosity of water and detecting submerged objects are investigated. An actual Brillouin lidar system is developed. Also, several basic problems related to Brillouin lidar are studied in detail. The attenuation coefficient of a pulsed laser beam with high pulsed energy in water is investigated; it is helpful to reveal the propagation property of a laser beam in water. The investigations on the threshold value of SBS are made theoretically and experimentally. Finally, a novel phenomena is investigated experimentally, in which Stimulated Raman scattering can be enhanced by stimulated Brillouin scattering.     

基于布里渊散射信号检测的大气探测模型

以激光信号在传输介质中的布里渊散射频移量模型为基础,依据相关大气数据建立基于布里渊散射信号检测的大气探测模型。该模型中布里渊频移量只与大气高度相关,详细描述了低空大气范围内布里渊频移量的连续分布状态。结果表明在086 km的海拔高度范围内,大气的布里渊散射频移量分布在1.01.3 GHz之间。与有关数据相比,该模型与实际情况非常符合,同时具有很好的连续性和普适性。     

Pressure dependence of the refractive index and of the sound velocity of methanol-ethanol solution: A Brillouin scattering study

Abstract

The pressure dependence of the refractive index n(P) and of the longitudinal acoustic velocities of 4.1 methanol-ethanol solution have been measured in a diamond anvil cell up to 8.1 GPa. We utilize Brillouin scattering methods for this determination and detect, in the same back scattering configuration, acoustic wave propagation parallel to the faces of the diamond anvils as well as along the incident laser radiation direction. We also deduce that the polarizability of the fluid is reduced by about 15% over the pressure range studied.     

Stimulated Brillouin scattering in dispersion-decreasing fiber with ultrahigh-speed femtosecond soliton pulse compression

We report that stimulated Brillouin scattering (SBS) in a dispersion-decreasing fiber (DDF) is particularly disadvantageous with ultrahigh-speed femtosecond soliton compression that exceeds 40 GHz. It is important to note that the increase in the longitudinal mode power of a soliton is proportional to the square of the repetition rate. The SBS threshold is determined by the dispersion-decreasing rate of the DDF, rather than its fiber loss. We suppressed the SBS by applying 30-MHz frequency modulation to a mode-locked fiber laser and successfully obtained a stable 40-GHz, 100-fs pulse train.     

熔石英棒-光纤构成的新型复合相位共轭镜的实验和理论研究

提出了一种新型的由熔石英棒和石英光纤组成的复合型相位共轭镜,其可运用于高重复频率激光输入系统中以改善光束质量.该复合相位共轭镜具有较高的受激布里渊散射反射率和受激布里渊散射损伤阈值以及较低的受激布里渊散射阈值等优点.实验中,在100 Hz重复频率下,最大获得了42.05%的受激布里渊散射反射率.根据实验条件,由耦合波方程及边界条件得到的物理模型,经数值求解后得到的结果和实验符合较好.且由理论结果提出了一种提高该复合型相位共轭镜工作状态的有效方法. 关键词： 复合型相位共轭镜 受激布里渊散射 熔石英 耦合波方程     

40-gHz, 100-fs stimulated-Brillouin-scattering-free pulse generation by combining a mode-locked laser diode and a dispersion-decreasing fiber

A 40-GHz, 100-fs pulse train was successfully generated by soliton compression of a mode-locked laser diode (MLLD) pulse with a dispersion-decreasing fiber. The MLLD had a longitudinal mode linewidth as broad as 60 MHz, which made it possible to suppress stimulated Brillouin scattering and achieve stable, ultrahigh-speed pulse compression without applying external frequency modulation.     

Widely tunable linear-cavity multiwavelength fiber laser with distributed Brillouin scattering

We demonstrate a multiple wavelength Brillouin/erbium fiber laser in a linear cavity configuration.The laser cavity is made up of a fiber loop mirror on one end of the resonator and a virtual mirror generated from the distributed stimulated Brillouin scattering effect on the other end.Due to the weak reflectivity provided by the virtual mirror,self-lasing cavity modes are completely suppressed from the laser cavity.At Brillouin pump and 1480-nm pump powers of 2 and 130 mW,respectively,11 channels of the demonstrated laser with an average total power of 7.13 dBm can freely be tuned over a span of 37-nm wavelength from 1530 to 1567 nm.     

Direct measurements of an increased threshold for stimulated brillouin scattering with polarization smoothing in ignition hohlraum plasmas

We demonstrate a significant reduction of stimulated Brillouin scattering by polarization smoothing in large-scale high-temperature hohlraum plasma conditions where filamentation is measured to be negligible. The stimulated Brillouin scattering experimental threshold (defined as the intensity at which 5% of the incident light is backscattered) is measured to increase by a factor of 1.7+/-0.2 when polarization smoothing is applied. An analytical model relevant to inertial confinement fusion plasma conditions shows that the measured reduction in backscatter with polarization smoothing results from the random spatial variation in polarization of the laser beam, not from the reduction in beam contrast.     

Theoretical Analysis of the Critical Phenomena of a Brillouin Laser

The critical phenomena of a Brillouin laser are analyzed theoretically. The results show that the behavior of a Brillouin laser in the threshold region is a second-order phase transition. The critical point of the phase transition is the gain threshold of the Brillouin laser, and the order parameter is the amplitude of the Stokes component in stimulated Brillouin scattering. The critical slow-down phenomenon and the typical characteristics in phase transition are demonstrated. Further work on the combination of nonlinear optics and phase transition in the Brillouin laser may lead to a new view and findings that could be significant for both fields.     

布里渊散射模式的确定

布里渊散射模式的确定王荣平ａ，ｂ刘玉龙ａ景强华ｂ曾令祉ｂ（ａ：中国科学院物理研究所，北京１０００８１）（ｂ：北京工业大学应用物理系，北京１０００２２）ＤｅｔｅｒｍｉｎａｔｉｏｎｏｆＢｒｉｌｏｕｉｎＳｃａｔｅｒｉｎｇＭｏｄｅｓＷａｎｇＲｏｎｇｐｉｎｇ...     

Amplification effect on SBS and Rayleigh scattering in the backward pumped distributed fiber Raman amplifier

The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fiber Raman amplifier （FRA） is studied. The pump source is a 1427.2-nm fiber Raman laser whose power is tunable between 0 - 1200 mW, and the signal source is a tunable narrow spectral bandwidth （〈 10 MHz） external cavity laser （ECL）. The Rayleigh scattering lines are amplified by the FRA and Stokes SBS lines are amplified by the FRA and the fiber Brillouin amplifier. The total gain of SBS lines is the production of the gain of Raman amplifier and that of Brillouin amplifier. In experiment, the SBS gain is about 42 dB and the saturation gain of 25-km G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.     

Stimulated Brillouin scattering-induced phase noise in an interferometric fiber sensing system

Stimulated Brillouin scattering-induced phase noise is harmful to interferometric fiber sensing systems. The localized fluctuating model is used to study the intensity noise caused by the stimulated Brillouin scattering in a single-mode fiber. The phase noise structure is analyzed for an interferometric fiber sensing system, and an unbalanced Michelson interferometer with an optical path difference of 1 m, as well as the phase-generated carrier technique, is used to measure the phase noise. It is found that the phase noise is small when the input power is below the stimulated Brillouin scattering threshold, increases dramatically at first and then gradually becomes flat when the input power is above the threshold, which is similar to the variation in relative intensity noise. It can be inferred that the increase in phase noise is mainly due to the broadening of the laser linewidth caused by stimulated Brillouin scattering, which is verified through linewidth measurements in the absence and presence of the stimulated Brillouin scattering.