Stimulated Raman scattering of lattice translational modes in liquid heavy water

A study was conducted on stimulated Raman scattering (SRS) when laser-induced plasma is formed in heavy water by focusing an intense picosecond pulsed Nd:YAG laser beam with wavelength 532 nm at room temperature. An unexpected 280 cm(-1) low frequency SRS line attributed to the lattice translational modes is observed. This SRS line and the internal-mode SRS lines indicate that the ice VII structure is formed in heavy water under the condition of laser-induced shockwave production.     

Stimulated Raman scattering of pre-gaussian light

The quantum theory of a forward Stokes generation by means of stimulated Raman scattering is considered in the case of a pre-gaussian pump composed by two and three telegraphs. As for the case of a colored chaotic pump the mean Stokes intensity is found to be enhanced over that resulting from a coherent pump in both transient and steady-state limits. In the limit that the pre-gaussian bandwidth becomes large, the mean Stokes intensity also becomes identical with that resulting from a coherent pump.     

Stimulated Raman scattering of light in artificial opal filled by water

We investigate stimulated scattering of light in globular photonic crystals infiltrated by water. Excitation of stimulated scattering of light is realized using powerful ultrashort (70 ps) laser pulses with an energy of 35 mJ and a frequency repetition of 15 Hz. We use the second-harmonic generation (532 nm) of the master oscillator and amplifier with a wavelength of 1064 nm. The photonic crystals under study are artificial opals filled by water or ethanol. We characterize the sample structures employing an electronic microscope along with the fiber-optics reflectance-spectroscopy technique. Photonic crystals have a stop band near the spectral positions of the exciting line (532 nm) and the first satellite of stimulated Raman scattering of light in water (649 nm). We observe a substantial reduction of the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices in comparison with that of pure water. Such a reduction is explained as the result of a sharp increase in the photonic density of states near the stop-band edges of investigated photonic crystals. The reduction in the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices opens up the opportunity to observe stimulated Raman scattering in numerous water media, including water solutions, biological and medical samples, heavy waters, and others.     

351nm激光入射大腔靶的受激Raman散射光谱

 报道了“神光 Ⅱ”装置上Au大柱腔靶产生的受激Raman散射光谱。通过分析实验条件和测量结果，排除了散射光谱来自增强非相干Thomson散射的可能性，发现用丝化不稳定性与受激Raman散射的耦合能合理解释观测到的Raman光谱。考虑到丝化不稳定性与SRS的耦合，测量到的散射光谱依然能用于密度诊断，其结果与对流SRS理论的计算值相差不到10%。     

351nm激光入射大腔靶的受激Raman散射光谱

报道了“神光 Ⅱ”装置上Au大柱腔靶产生的受激Raman散射光谱。通过分析实验条件和测量结果,排除了散射光谱来自增强非相干Thomson散射的可能性,发现用丝化不稳定性与受激Raman散射的耦合能合理解释观测到的Raman光谱。考虑到丝化不稳定性与SRS的耦合,测量到的散射光谱依然能用于密度诊断,其结果与对流SRS理论的计算值相差不到10%。     

Stimulated Raman scattering and four-wave Raman mixing seeded by a supercontinuum generated in dibromomethane using picosecond and femtosecond laser sources

Stimulated Raman emission from liquid dibromomethane (vibrational Raman shift frequency, 588 cm⁻¹) is introduced into hydrogen gas (rotational Raman shift frequency, 587 cm⁻¹) as a seed beam, in order to generate numerous rotational lines by four-wave Raman mixing. Unexpectedly, a supercontinuum, which is generated by self-phase modulation in dibromomethane, acted as a seed beam to exclusively generate vibrational lines; the rotational lines are generated only when the supercontinuum is minimal. The former is explained by a competition between the high-gain vibrational and low-gain rotational Raman effects when strongly seeded by a supercontinuum. The latter is explained by stimulated Raman gain under the seed effect exclusively to the first-Stokes rotational line.     

光解产生的铅原子中受激喇曼散射和共振激光辐射

用2660(?)的紫外激光解离PbCl_2分子时,发现在3740(?)和3734(?)波长上有较强的受激辐射输出.根据它们的光谱特性和铅原子的能级结构判断,这些辐射是基于双光子解离PbCl_2分子得到的铅原子在6p~(23)P_2亚稳能级上的布居而产生的光泵共振激光辐射和受激喇曼散射.提出了描述整个过程的理论模型,通过拟合实验结果,确定了2660(?)激光双光子解离PbCl_2产生6p~(23)P_2亚稳态铅原子的光解系数.当PbCl_2分子密度为N_(00)=6.21×10~(16)cm~(-3)时,光解产生的铅原子在6p~(23)P_2和6p~(21)D_2这两个亚稳态的最大布居数近似相等,称为2.0×10~(16)cm~(-3).     

Stimulated scattering of light in a laser produced magnetoplasma

This note considers stimulated scattering of laser light in the ordinary mode by magnetosonic waves in a plasma. Problems of three-wave decay interaction and modulation instability are investigated. The growth rates and thresholds are obtained analytically. Application to laser-plasma interaction is discussed.     

Stimulated Raman scattering of gaussian laser beam in relativistic plasma

This paper presents an investigation of Stimulated Raman Scattering of gaussian laser beam in relativistic Plasma. The pump beam interacts with a pre-excited electron plasma wave and thereby generate a back-scattered wave. Due to intense laser beam, electron oscillatory velocity becomes comparable to the velocity of light, which modifies the background plasma density profile in a direction transverse to pump beam axis. The relativistic non-linearity due to increase in mass of the electrons effects the incident laser beam, electron plasma wave and back-scattered beam. We have set up the non-linear differential equations for the beam width parameters of the main beam, electron plasma wave, back-scattered wave and derived SRS back-reflectivity by taking full non-linear part of the dielectric constant of relativistic plasma with the help of moment theory approach. It is observed from the analysis that self-focusing of the pump beam greatly affects the SRS reflectivity, which plays a significant role in laser induced fusion.     

双包层光纤激光器的受激拉曼散射与热应力

 建立了高功率掺镱双包层光纤激光器的速率方程模型与热应力模型,对影响受激拉曼散射效应和热应力效应的关键参数（如纤芯半径、光纤长度、泵浦波长、泵浦方式）进行了数值模拟。结果表明:对于较小的纤芯半径,光纤内的斯托克斯光功率较大且增长迅速,因此增加纤芯半径能有效减弱受激拉曼散射效应;减小光纤长度能提高受激拉曼散射的阈值,而纤芯的热应力也增大,因此在不出现热应力引起光纤断裂的情况下,可以减小光纤长度以提高输出功率;采用976 nm波段泵浦源能提高输出功率,降低热应力的影响;两端均匀泵浦方式可以有效降低纤芯热应力,同时维持高功率输出。     

水的低频受激拉曼散射

利用532 nm的脉冲激光进行了水的受激拉曼散射研究. 水的低激发光能量下主要表现为受激Stocks和反Stocks 3426 cm^-1谱线; 在能量大于140 mJ时出现低频率313 cm^-1受激Stocks谱线, 同时出现后向3389和3268 cm^-1 的受激Stocks谱线. 实验结果表明, 在较强的激光作用下, 水的结构表现为冰的Ⅷ相.     

水的低频受激拉曼散射

利用532 nm的脉冲激光进行了水的受激拉曼散射研究. 水的低激发光能量下主要表现为受激Stocks和反Stocks 3426 cm^-1谱线; 在能量大于140 mJ时出现低频率313 cm^-1受激Stocks谱线, 同时出现后向3389和3268 cm^-1 的受激Stocks谱线. 实验结果表明, 在较强的激光作用下, 水的结构表现为冰的Ⅷ相.     

Stimulated resonance Raman scattering

A quantum mechanical theory of stimulated resonance Raman scattering taking full account of the effects of the incident and scattered radiation on the state and properties of the molecules is developed. The resulting formulas enable the amplification of the scattered radiation and the attenuation of the incident flux to be determined. The conditions under which stimulated Raman scattering produces amplification of radiation are formulated. The range of applicability of the theory, not taking account of the effects of radiation on the properties of the material is discussed.     

Stimulated Raman scattering of barium laser output in a silica fibre

Strong stimulated Raman emission has been observed on three Stokes' lines at 1.608, 1.744 and 1.896m from 12.6 km of single-mode silica fibre pumped at 1.50m with the output of a pulsed barium vapour laser. A study has been made of the spectral distribution of fibre output as a function of peak input power to the fibre (up to 47 MW cm^–2), and the results are compared to theoretical predictions. Incomplete conversion of the pump to first Stokes', and first to second Stokes', lines is observed despite the length of the fibre.     

Stimulated Raman scattering of copper vapour laser radiation in optical fibres

Wideband frequency conversion of copper vapour laser radiation has been achieved by stimulated Raman scattering in multimode silica fibres. Up to nine Stokes' orders have been generated in the 511 to 649 nm spectral region with a conversion efficiency greater than 90% of the fibre output. Four-wave mixing processes involving laser and Stokes' lines have also been observed.     

Stimulated Raman scattering and spontaneous Raman solitons in ammonia

In this study we report the first observation of spontaneous Raman solitons in stimulated Raman scattering (SRS) by the gas NH₃. The scattered radiation is called Stokes radiation. Raman solitons are of considerable interest, because their existence can be explained by quantum-mechanical fluctuations of the electromagnetic field in vacuum. We have observed spontaneous Raman solitons in a forward SRS configuration for two different molecular transitions of NH₃, the laser emissions at 58 μm and 72.6 μm wavelength. These are optically pumped by 10 μm CO₂-laser pulses with a duration of 100 ns and an energy of 150 mJ. Spontaneous Raman solitons are short spikes in the pump pulse which occur during its depletion. Their origin is the rapid π phase change of the Stokes seed. In contrast to other laboratories we have used single-pass cells. Thus, we have succeeded in observing multiple spontaneous Raman solitons during one pump pulse. Previous experiments with multi-pass cells never showed multiple solitons. Since multiple spontaneous Raman solitons have already been reported in an earlier experiment with a single-pass cell filled with hydrogen at high pressure, we conclude that such multiple Raman solitons can be observed mainly in this type of gas cell. Subsequently, we have performed statistical measurements on the delay time and the height of the spontaneous Raman solitons in the depleted pump pulse for the 58 μm-NH₃ emission. We have compared these statistics with theory and equivalent experimental results of other laboratories. They are in good agreement with the assumption that quantum-mechanical fluctuations are the origin of spontaneous Raman solitons. The most recent theories postulate that the origin of the formation of spontaneous Raman solitons can be explained by the rapid π phase change of the Stokes seed as well as that of the laser or polarization wave. Therefore, we have determined the phase of the spontaneous Raman solitons relative to the depleted pump pulse. Although, such changes of sign of the relative phase have already been observed in an earlier SRS experiment with hydrogen at high pressure, we did not detect any in our experiment. Therefore, we conclude that in this experiment the π phase change occurs in the Stokes or polarization wave.     

Measurement of the shape of picosecond light pulses using stimulated Raman scattering

The vibrational amplitude and the intensity of the Stokes light generated by transient stimulated Raman scattering rise and decay very rapidly. The time duration of the Stokes pulse and of the phonon pulse is much shorter than the pump pulse duration. It is shown that both phonon and Stokes pulses can be used to probe the shape of ultrashort light pulses.     

Stimulated Raman backward scattering of a laser beam in a magnetized plasma

Stimulated Raman scattering of a laser beam is investigated in the plasma with strong self generated magnetic field. The magnetized plasma supports various localized radial and azimuthal modes of lower hybrid frequencies. The density fluctuations due to lower hybrid modes couple with the oscillating velocity due to the pump, and drive the scattered wave. Equations describing the Raman process are derived and effects of various modes are studied on the growth rate analytically. Self generated magnetic field has a strong localization effect on the Raman process and growth rate is maximum for radial eigen mode number q = 0 and azimuthal eigen mode number l = 3. The frequency shift has signatures of self generated magnetic field and could serve as a diagnostic.     

高功率双包层光纤激光器受激拉曼散射和热效应的理论研究

 受激拉曼散射和热效应会限制光纤激光器功率的提高。利用高功率光纤激光器的速率方程和热传导方程,理论研究了双端泵浦和分布泵浦下双包层光纤激光器的受激拉曼散射和热效应,得到了光纤中的泵浦光、激光和斯托克斯光的功率分布,光纤激光器的输出特性以及光纤中的温度分布。分析表明,当泵浦功率增大到一定值时,光纤激光器中出现SRS,一部分激光功率会转移给斯托克斯光,影响激光功率进一步提高;与双端泵浦方式相比,分布泵浦下光纤激光器的斜率效率和最大输出功率相差不大,但是,光纤中的温度分布被有效地降低,因此,分布泵浦方式更为有效。     

高功率双包层光纤激光器受激拉曼散射和热效应的理论研究

受激拉曼散射和热效应会限制光纤激光器功率的提高。利用高功率光纤激光器的速率方程和热传导方程,理论研究了双端泵浦和分布泵浦下双包层光纤激光器的受激拉曼散射和热效应,得到了光纤中的泵浦光、激光和斯托克斯光的功率分布,光纤激光器的输出特性以及光纤中的温度分布。分析表明,当泵浦功率增大到一定值时,光纤激光器中出现SRS,一部分激光功率会转移给斯托克斯光,影响激光功率进一步提高;与双端泵浦方式相比,分布泵浦下光纤激光器的斜率效率和最大输出功率相差不大,但是,光纤中的温度分布被有效地降低,因此,分布泵浦方式更为有效。