固体三倍频激光在高压H2中受激拉曼散射的实验研究

利用Nd∶YAG激光器的三倍频输出 (35 5nm)在H2 中的受激拉曼散射 (SRS)获得波长在 2 0 4～ 86 7nm范围内的激光输出。当抽运能量为 70mJ时观察到四阶Stokes光和五阶Anti Stokes光 ,其中第一阶Stokes光 (416nm)输出能量为 2 8 7mJ,第二阶Stokes光 (5 0 3nm)输出能量为 16mJ,一阶Anti Stokes光 (30 9nm)输出能量为 3mJ。研究了H2 压力和各阶Stokes光能量的关系 ,同时观察到环行光斑和脉宽压缩现象。     

基于拉曼晶体的多波长激光技术研究进展

利用受激拉曼散射效应,以拉曼晶体作为介质,可产生同轴输出的多波长激光信号,该种激光器具有结构紧凑、脉冲能量高和波长可调谐等特点,在全色激光成像与显示、光电对抗等领域有着重要的应用前景。本文介绍了受激拉曼散射基本原理和常用拉曼激光器结构,研究了国内外基于拉曼晶体的多波长激光技术的研究进展,总结了利用受激拉曼散射产生多波长激光存在的不足。针对目前受激拉曼散射高阶散射光较难生成,生成的多波长激光信号覆盖谱段较窄,输出功率较低,调谐方式单一等问题,提出了今后多波长激光技术发展方向。     

Nd:YAG四倍频激光抽运D2和D2/He受激拉曼散射的实验研究

使用脉冲Nd:YAG四倍频激光抽运充有纯D2气体和D2/He混合气体的拉曼池.实验研究了受激拉曼散射的能量转换效率和能量稳定性与系统主要参量,包括抽运光能量、D2气体压强和加入惰性气体He的关系.实验表明,适量惰性气体He的加入在没有降低一阶斯托克斯散射光(S1,波长:289.04 nm)能量稳定性的前提下,有利于提高其能量转换效率,最大能量转换效率达到22.1%.通过实验分析,得到了受激拉曼散射一阶斯托克斯散射光的能量转化效率和能量稳定性的优化条件.     

红宝石激光泵浦的高压氢受激Raman散射实验研究

介绍观察受激 Raman 现象的实验系统和实验结果。测定了产生受激 Raman 散射的激光能量阈值和各级散射光的转换效率。结果表明,受激 Raman 散射是多个波相互作用的参量过程。     

宽带抽运情况下乙醇、丙酮溶液中受激拉曼散射光谱的实验研究

研究了乙醇、丙酮两种拉曼介质在宽带抽运情况下啁啾激光脉冲的受激拉曼散射频谱特性 ,得到的一级Stokes光频谱宽度与抽运光基本相当 ,且具有较高的转换效率 ,从而表明了利用“展宽—受激拉曼散射—压缩”的办法获得波长近 1μm的飞秒级超短脉冲激光信号源的实验方案具有可行性     

高压甲烷的受激喇曼散射研究

我们研究了高压甲烷的受激喇曼散射,泵浦激光为Nd:YAG调Q脉冲激光,得到一阶斯托克斯散射光,脉冲能量达到20mJ,并观察到1至5阶反斯托克斯散射波。     

脉冲光布里渊散射信号的拉曼放大研究

实验研究了前向拉曼泵浦方式下脉冲信号光产生的自发布里渊散射信号和受激布里渊散射(SBS)信号的拉曼放大规律。拉曼泵浦放大自发布里渊散射信号时,随泵浦功率增大会出现SBS现象,对散射信号的放大由拉曼放大和布里渊放大两部分引起,因此增益较大,当拉曼泵浦功率为1 000 mW时Stokes光增益可达54 dB。拉曼泵浦放大SBS信号时,放大过程中只存在拉曼放大。且当泵浦功率增大至600 mW时,会引起多级布里渊散射,致使一级Stokes和泵浦能量会转移到下一级布里渊散射,一级Stokes光增益饱和并下降。     

受激布里渊散射光束空间光强分布

将调Q的Nd:YAG激光脉冲聚焦到FC-72介质池中,利用电荷耦合器件(CCD)和数字图像处理技术,实验研究了后向受激布里渊散射(SBS)光斑的光强分布,获得了其光强分布及光斑大小随入射能量的变化规律。结果表明,在入射光束为基模高斯光束的条件下,随着入射光能量增大,受激布里渊散射光斑的空间光强分布由近高斯型变为高斯型。并且受激布里渊散射光斑大小总体上是随着入射光能量的增大而逐渐减小的。当入射能量在受激布里渊散射阈值附近时,受激布里渊散射光斑大小达到最大(大于入射光斑);当入射能量为3倍阈值以上时,受激布里渊散射光斑大小达到最小(小于入射光斑)。     

CH4受激拉曼散射产生紫外激光用于NO2差分吸收激光雷达的研究

脉冲Nd:YAG三倍频激光(355 nm)泵浦CH4的受激拉曼散射第一级斯托克斯光(395.6 nm)用作NO2差分吸收激光雷达的λon.为研究CH4的受激拉曼散射效应和定量解释其物理机理作了数值模拟计算,并作了一系列的实验.通过调节泵浦能量、光束质量和气体压强,得到了各级散射光的能量转化效率与三者间的函数关系,找到了第一级斯托克斯光的优化条件.     

掺镱全光纤激光振荡器横向模式不稳定与受激拉曼散射的关系

研究了掺镱全光纤激光振荡器中横向模式不稳定效应与受激拉曼散射之间的关系。在纤芯直径为20μm的单端抽运1.5kW级全光纤激光振荡器中,当受激拉曼散射达到一定阈值时,横向模式不稳定效应突然出现,激光器输出功率突然减小,减小的输出功率由包层光滤除器倾泻到谐振腔外。实验发现:受激拉曼散射光谱增强、输出功率减小与包层光滤除器温度上升存在一定的关联;通过缩短光纤长度抑制受激拉曼散射,可以将单端抽运激光振荡器的横向模式不稳定阈值增大到2kW以上。对纤芯直径为25μm的双端抽运激光振荡器进行研究,同样通过抑制受激拉曼散射增大了横向模式不稳定阈值,获得了大于5kW的激光功率输出。实验结果初步验证了在非线性较强的情况下,受激拉曼散射是导致横向模式不稳定的原因,通过抑制受激拉曼散射可以增大横向模式不稳定阈值。     

四倍频Nd：YAG激光在高压氢气中的喇曼频移研究

利用Nd:YAG固体激光器四倍频输出(266nm)在高压H₂中的受激喇曼散射获得多波长的激光输出。当泵浦能量一定时,通过改变H₂压力得到了最佳的能量输出,299nm波长的激光能量为3mJ,341nm波长的激光能量输出为6.1mJ,398nm波长的激光能量输出为2.8mJ,239nm波长的激光能量输出为0.8mJ,同时在477nm,595nm,218nm,200nm波段也有能量输出。     

光纤中的多级斯托克斯及反斯托克斯谱线

本文叙述在多模光纤中产生的多级受激拉曼散射谱，作了两种不同掺杂的SiO2光纤中的受激拉曼散射谱。对掺锗硅光纤得到16级斯托克斯线及10级反斯托克斯线。对掺磁硅光纤获得了13级斯托克斯线及4～5级斯托克斯线。测出了各级谱线的峰值波长及相对强度分布，并作了简单讨论。     

VUV generation by high-order CARS

Generation of VUV (vacuum ultraviolet) radiation by stimulated Raman scattering (SRS) in H₂ is studied with collinear irradiation of the first Stokes component simultaneously with pump laser radiation. Improvements of the high-order coherent anti-Stokes Raman scattering (CARS) method over the pure SRS scheme are: generation of higher anti-Stokes (AS) orders, increased conversion efficiency, and considerably better reproducibility. Experimental results are presented to confirm the theoretical analysis     

Nd:YAG四倍频激光抽运氘后的拉曼效应及其在激光雷达中的应用

利用 Nd:YAG四倍频激光抽运氘气 (D2 )的受激拉曼效应 ,获得一阶斯托克斯 (Stokes)波长2 89nm。通过改变拉曼介质 D2 气压与抽运光能量 ,获得了一阶斯托克斯输出的较佳条件。该波长与 Xe Cl准分子激光波长 30 8nm采用差分吸收方法 ,建立了用于对流层臭氧探测的激光雷达 ,并初步获得了对流层大气臭氧的垂直分布及其时间变化特征。     

Stimulated Raman Scattering in Nanorod Silicon Carbide Films

When the film is excited by a very low excitation energy, the spontaneous Raman scattering emerges. The intensity of Raman scattering is proportional to the excitation power below the threshold excitation. When the excited power reaches the excitation threshold, the intensity of Stokes light strongly increases. Meanwhile an anti Stokes light at 495 nm and multiple order but small Stokes peaks occur. The intensity of Stokes light is much larger than that of anti Stokes. The full width of half maximum (FWHM) of Stokes peak is reduced from 0.4 nm to less than 0.2 nm, the scattering angle between both Stokes and incident lights becomes less than 1°, and the angle between the Stokes and anti Stokes lights is about 3°. When the exciting power is in excess of the threshold, anti Stokes and multiple Raman scattering peaks reappear. These experiments can be unlimitedly repeated. From this experiment, we can exclude the possibility of spontaneous Raman scattering. It is suggested that the nanorods are a quantum line dimension having a large surface. There will be Raman differential scattering section so long as the nanorod films become very strong scattering media; the surface enhanced Raman scattering will be produced, the nanorod films of SiC will form a strong multiple scattering resonance cavities so as to form the stimulated Raman scattering oscillation.     

Studies of the spatial distribution and beam quality of Stokesoutput from a Raman generator pumped by a broad-band KrF laser

One-dimensional stimulated Raman scattering (SRS) theory is extended to three dimensions by the concept of transverse modes associated with the Fresnel number. Two simplified models are introduced to evaluate the beam parameters and waist position under low gain. The dependence of waist size and position of the Stokes beam on the focus position and Rayleigh length of the focused pump laser is analyzed and verified by experiment. The Fresnel number approach is utilized to evaluate the energy density distribution and the mode structure of the pump laser in a Raman cell under high gain. The different configurations are classified and relevant mode formulation and spatial distribution are discussed. The experimental result shows that the beam quality of the Stokes output from a Raman generator depends essentially on the pump configuration and the geometric parameters of the pump laser and is insensitive to the practical pump power, which agrees with the theoretical analysis. The results obtained are adopted to improve the beam quality of the first-order Stokes output from the Raman generator with different configurations     

Numerical Modeling of Pulsed Raman Fiber Converters at 2 $mu{hbox {m}}$

Theoretical modeling of stimulated Raman scattering (SRS) in fibers is presented for the near-infrared band around 2 mum, where pump and Stokes wave have different absorption. This model takes into account amplified spontaneous emission (ASE), SRS towards Stokes and anti-Stokes waves, absorption of the Raman medium and Rayleigh backscattering in fibers. Depending on the fiber configuration, this model includes the cavity parameters of either external or internal mirrors at the fiber ends. Input parameters are, among others, temporal profiles of the pump radiation, absorption, and gain curve of the Raman medium. The model agrees well with experimental results obtained with a GeO₂ doped core fiber pumped by a pulsed and tunable Tm:silica fiber laser emitting around 2 mum.     

Subnanosecond pulse generation in the VUV by dual-wavelength pumpedstimulated rotational Raman scattering

A novel scheme to generate a subnanosecond pulse in VUV spectral region is proposed, by applying a dual-wavelength pumping method in conjunction with polarization switching technique to the stimulated rotational Raman scattering process. Optimum conditions for the efficient conversion and short pulse generation are presented through numerical model calculations. It is theoretically shown that the duration of the first anti-Stokes pulse of a VUV pump laser can be shorten to 0.72 ns. Since the anti-Stokes pulse is generated at a frequency within the gain profile of the pump laser, the proposed process is applicable to a seed pulse generation for subnanosecond pulse amplification by the pump laser medium in the VUV region     

Stokes-Anti-Stokes Iterative Resonator Method for Modeling Raman Lasers

We present a novel modeling method to describe the steady-state and transient regimes of a continuous-wave pumped Raman laser emitting both Stokes and anti-Stokes photons. Our so-called "Stokes-anti-Stokes iterative resonator method" evaluates for every half round-trip time the longitudinal distribution of the intracavity pump, Stokes and anti-Stokes fields propagating in forward and backward directions. Although this Stokes-anti-Stokes iterative resonator method is widely applicable, its most important asset resides in its ability to accurately model Raman lasers that feature cavity enhancement of the pump power and that emit both Stokes and anti-Stokes photons. Important here is that our modeling method correctly incorporates the longitudinal intracavity field distributions, the generation of anti-Stokes photons, and the interference effects between incident and intracavity pump fields, and that it describes not only the lasers' steady-state operation but also their transient characteristics. We demonstrate for both a hydrogen-based and a silicon-based Raman laser with pump cavity enhancement that the Stokes-anti-Stokes iterative resonator method performs better than the modeling methods presently used for these categories of Raman lasers. Finally, to demonstrate the potentialities of our modeling method, we numerically simulate, for the first time according to our knowledge, the anti-Stokes emission generated by a silicon-based Raman laser