Compression of ultraintense laser pulses in inhomogeneous plasma upon backward stimulated raman scattering

The potential for time compression of ultraintense laser pulses in plasma based on nonlinear interactions between waves during backward stimulated Raman scattering is analyzed analytically and numerically. The optimal conditions for obtaining a maximal energy conversion coefficient of 10-ps laser pulses to the energy of 100-fs Stokes pulses are found.     

Inverse resonance raman scattering and resonance raman amplification

The characteristics of Inverse Resonance Raman Scattering (IRRS) and Resonance Raman Amplification (RRA) are discussed. Both effects have been experimentally examined using an intracavity arrangement. With this technique which has a time resolution of 30 ns it was possible to obtain Raman lines from highly fluorescent dyes which were present in concentrations down to 10^-6 mole/

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基于后向散射模型的蒸汽湿度测量及仿真

为了更加准确地测量出汽轮机末级蒸汽湿度,为锅炉给水量提供依据,促进汽轮机内部除湿技术的发展,采用了后向角散射法的思路设计了湿蒸汽参数测量模型,并对模型所需物理量进行了详细的计算,为后向散射法测量蒸汽湿度的研究提供参考。通过对模型进行仿真模拟以及实验研究,得到了后向散射光光强数据。通过对比仿真模拟数据与实验数据,验证了该模型的可行性与有效性,对光散射法测量蒸汽湿度的实验分析以及工程实践具有重要意义。     

基于增强拉曼散射的光子-原子双模压缩态的实现

拉曼散射过程中利用原子系综中初始制备的自旋激发(原子相干性),以及注入与原子系综中初始制备的自旋激发相关联的种子光场都可以极大的提高光场频率转换的效率,实现增强拉曼散射.本文理论上计算了增强拉曼散射过程中原子-光场量子界面的正交分量的量子起伏,得到了相干性导致的增强拉曼散射,只能在一定的范围内稍微提高初始光子-原子的压缩度;而关联增强拉曼散射,能够制备很强的光子-原子间的双模压缩.这样强压缩度的光子-原子量子界面,对于利用光场和原子系统实现量子精密测量研究有着非常重要的应用.     

Vacuum-stimulated raman scattering based on adiabatic passage in a high-finesse optical cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counterintuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a subnatural linewidth. The results are in excellent agreement with numerical simulations.     

Kilohertz raman lasers based on bno and kgw crystals for a wide spectral range

Efficient Raman lasers based on Ba(NO₃)₂ and KGd(WO₄)₂ crystals which produce nanosecond pulses with repetition rates of 1 and 4 kHz at 26 wavelengths between 280 and 1600 nm are developed and studied. A maximum SRS conversion efficiency of 25% is obtained. It is found that the divergence of the beams generated by the Raman laser can be significantly reduced by using quasi-Bessel pump beams and an unstable telescope cavity.     

Stimulated raman scattering of fuel droplets

The strong stimulated Raman scattering (SRS) from diesel fuel droplets has the potential of providing the relative concentration of multicomponent fuel and the absolute size of individual droplets. The morphology-dependent resonances (MDRs) of a sphere cause the droplet to act as an optical resonator which greatly lowers the SRS threshold. The number density, quality factor, and frequency shift of several MDRs are calculated as a function of the ratio of the index of refraction of the liquid and the surrounding gas, which approaches unity at the thermodynamic critical condition for the fuel spray. The SRS spectra of monodispersed droplets of toluene, pentane, Exxon-Aromatic-150, and Mobil D-2 are presented. The exponential growth region of the SRS intensity I _1S as a function of the input laser intensity I _input is investigated for the toluene carbon ring breathing mode v ₂ and the pentane C-H stretching region. The I _1S ratio of toluene and pentane is measured as a function of the ratio of the toluene and pentane concentration for monodispersed droplets. The reduced fluctuation in I _1S when I _input is changed from multimode to single-mode is displayed as a histogram of the I _1S of the v ₂ mode of toluene droplets.     

Doppler-free resonances of the second-order raman scattering

The possibility of the observation of Raman scattering resonances completely free from the influence of the Doppler effect has been examined for the first time. The phenomenon is based on the excitation of a Raman oscillation standing wave in a gas by two standing light waves, whose frequency difference is equal to half the Raman frequency. The complete compensation of Doppler shifts results from the simultaneous interactions between atomic particles and two pairs of counter-propagating waves. Doppler-free resonances of the second-order Raman light scattering appear in the number of particles excited to the upper Raman level and in the radiation at the Stokes and anti-Stokes frequencies. The amplitude estimate for the resonance in the number of particles is given for the example of neon.     

Observation of stimulated raman scattering in CVD-diamond

We report the first experimental observation of a nonlinear laser effect, stimulated Raman scattering (SRS), in manmade diamond grown from the gaseous phase by the chemical vapor deposition (CVD) technique. Multiple Stokes and anti-Stokes generation in the visible and near-IR ranges was excited under nanosecond and picosecond pumping in a 350-μ-thick plate. All the registered Raman-induced lasing wavelengths were identified. We classify the CVD-diamond as a promising χ⁽³⁾-active material for Raman laser converters in a record wide spectral range.     

Asymptotic behaviour of backward elastic scattering

We discuss a compact formula proposed by Dias de Deus and Pimenta for the asymptotic value of the elastic scattering amplitude at backward angles. Improvements and generalization are obtained by means of the saddle-point method which corroborate old calculations by Serber.     

Fröhlich coherent vibrations and raman scattering

Coherent vibration systems are very likely composed of oscillating protein molecules located in the closed surface of the plasma membrane. Except short periods in the cell life, the distribution of the oscillating molecules corresponds to the condition of the minimum energy of the generated electromagnetic field. In this case the Raman scattering is hardly possible.     

Enhanced adsorbate raman scattering and surface plasmon radiation

We present the first experimental results which demonstrate a quadratic relationship between the enhanced Raman scattering from molecules on Ag surfaces and roughness-coupled surface-plasmon radiation. These results are interpreted by a model which includes both roughness assisted surface-plasmon scattering and radiative coupling.     

Resonant interband raman scattering in metals and semimetals

A resonance has been observed in the Raman cross section for scattering from intralayer phonons in the quasi two-dimensional, metallic graphite intercalation compounds. The resonance is found to occur for photon energies which coincide with the threshold for electronic interband absorption. The cross section is observed to correlate with the frequency derivative |dϵ₂/dω|², where ϵ₂ is the imaginary part of the dielectric function. Theoretical calculations suggests the resonance should be observed in all Raman-active metals and semimetals.     

Photon echoes and site-selective raman scattering of samarium-vacancy dipoles

Abstract

Electronic Raman scattering of Sm²⁺ in KCl is performed under resonant interconfigurational excitation around 500 nm. The position of the charge-compensating cation vacancy with respect to the substitutional Sm²⁺ ion is derived from both the Stark splitting of the J-levels and the polarization properties of the scattered light. The influence of the different site symmetries on the optical linewidth is investigated with photon echoes, stimulated from an accumulated grating, which is built up under intraconfigurational excitation between the ⁷ F ₀ and the ⁵ D ₁ terms of the 4f ⁶5 _s ²5 _p ⁶ ground state configuration. The echo decay time is about 10 ps and does not change sizably when tuning the excitation frequency over the inhomogeneous distribution. This shows that for zero-phonon line excitation, the Sm²⁺ sites are not very different. The temperature dependence of the echo is described by vertical relaxation to the bottleneck under multi-phonon emission.