Quasi-Elastic Light Scattering in Congruent Lithium Niobate Crystals

Raman scattering spectra in the frequency range of 5–75 cm^–1 in lithium niobate samples with various structural imperfections were obtained. It is shown that the intensity of quasi-elastic light scattering on the wing of the Rayleigh line demonstrates an exponential dependence on the concentration of large-scale defects in the samples. Calibration curves for the intensity of quasi-elastic scattering dependence at low frequencies on the acoustic quality factor are constructed.     

Rayleigh and Raman scattering from optically active molecules

The intensity of Rayleigh and Raman scattering from optically active molecules is shown to be slightly different in right and left circularly polarized incident light. The circular intensity differential of the Rayleigh line is dependent on components of the optical activity tensor, and that of the Raman lines is a function of the variation of the optical activity with the vibrational coordinates. This circular intensity differential might be of the order of 10^-3 times that of the Rayleigh or Raman intensity.     

Raman and Rayleigh spectroscopy and molecular motions

Raman and Rayleigh scattering experiments on HCl, DCl, HBr and DBr molecules (pure liquid or isotopically diluted) have been carried out at room temperature. Results are discussed in the light of the existing theories on molecular motions in the liquid phase. The comparison of Rayleigh and Raman scattering results shows that reorientational processes are not sufficient to explain completely the profile of anisotropic Raman scattering. According to a recent theory due to Bratos, the rotational correlation function can be obtained only after elimination of the vibrational correlation function determined from the isotropic Raman scattering. In this last case broadening may arise from three causes: translational motion, resonance broadening and vibration-rotation coupling. A comparative study of the band profile of anisotropic Rayleigh and Raman scattering shows that the wings in both cases come from essentially the same origin while a band moment analysis is consistent with Gordon's theory according to which they are of reorientational origin.     

Estimation of Rayleigh scattering loss in a double-clad photonic crystal fiber

In this paper the effect of photonic crystal fiber’s structure parameters on Rayleigh scattering was investigated. Rayleigh scattering loss (RSL) has been numerically estimated by average Rayleigh scattering coefficient based on the empirical relations for \(V\) and \(W\) parameters of double-clad photonic crystal fibers (DC PCFs). The dependence of RSL on the two structural parameters—the air hole diameter and the hole pitch was demonstrated. We have shown that RSL depends on the index profiles because of the different optical power confinement factors in every layer of DC PCF. Using these results, the RSL can be optimized by adjusting the fiber parameters—air-hole diameter as well as the air-hole pitch.     

On the curve of the density of phonon states for cubic boron nitride (from the results of photoluminescence measurements)

The fine structure of the phonon wing associated with the zero-phonon line (ZPL) of the BN1 center in the cubic boron nitride is analyzed in comparison with the structure of the phonon wing of the luminescence center at 3.188 eV in diamond, the second-order Raman scattering spectrum, and the theoretically calculated densities of phonon states of the c-BN compound. Taking into account the similarity of the structures of the phonon wings in the spectra of the above centers and the previously made assumptions that the structure of the phonon wing of the center at 3.188 eV is due to the specific features in the density of phonon states of diamond, it is assumed that, in the observed density of phonon states of cubic boron nitride, the critical points are represented by the specific features of the structure of the phonon wing associated with the zero-phonon line (at 3.294 eV) of the BN1 luminescence center. In turn, these latter specific features coincide accurate to within 5–10cm^?1 with the theoretically calculated lattice vibrations of the c-BN compound and the experimental data obtained from the second-order Raman spectra.     

The temperature dependence of the Rayleigh line wing and depolarized combinational scattering line widths in critical mixtures

It has been experimentally found that at approaching the critical temperature of the exfoliating mixture carbon-disulfide-ethanol the widths of the Rayleigh line wing and the depolarized combinational scattering line drastically decrease. The same phenomenon was observed for 3 nitrobenzene combinational line scattering in a nitrobenzene—n-hexane mixture.     

Ionic contribution to Rayleigh line wing under conditions of light scattering by liquid electrolytic solutions

A theoretical treatment is performed of the mechanism (suggested in N. F. Bunkin andA. V. Lobeev, Z. Phys. Chem. 214, 269 (2000)) of ionic effect on the Rayleigh line wing under conditions of light scattering by liquid electrolytic solutions. The mechanism consists essentially in that the fluctuation electric field caused by Brownian motion of ions dissolved in a liquid leads, because of the Kerr polarization effect, to fluctuations of optical anisotropy of the scattering medium. The spectral characteristics of the Rayleigh line wing are obtained using the fluctuation-dissipative theorem as applied to equilibrium thermal electromagnetic field. Expressions are derived for the integral intensity and spectral width (Δν) of the Rayleigh line wing in terms of parameters of liquid solution such as the temperature T, the viscosity η, the concentration of dissolved ions n _i, and the coefficient of their diffusion D _i. It is demonstrated that Δν ∝ exp(?W/2T), where W is the activation energy of ion mobility b _i = D_i/T. The possible region of validity of developed theoretical concepts as applied to the experimental data for the Rayleigh line wing in electrolytic solutions is discussed.     

Rayleigh scattering from a trapped bose condensate and the corresponding recoil atom velocity distribution

An approach has been developed that allows the Rayleigh scattering cross section to be calculated with allowance for the quantum character of motion of the center of mass of the trapped scattering particles. The shape of the line of light scattering from a Bose condensate in a parabolic trap has been studied. A shift of the scattering line center is equal to the recoil shift, while the line width depends on the chemical potential of the Bose gas and on the relaxation time of the velocity of the above-condensate recoil particles. A velocity distribution function in the beam of recoil atoms formed in the course of induced Rayleigh scattering is determined. It is shown that, under the typical experimental conditions, the characteristic width Δv/v of the recoil velocity distribution in this beam is on the order of 10^?3 at a velocity v on the order of several centimeters per second.     

Spectra of molecular light scattering in guaiacol

The propagation velocity and absorbance of longitudinal hypersound weremeasured in a wide temperature range by scattered light spectra in pure guaiacol. The Rayleigh line wing spectrum was studied and the relaxation time of anisotropy fluctuations was determined. The temperature dependence and value of the molecular viscosity of guaiacol were determined from the data on the Rayleigh line wing width.     

Dynamical response and H-bond effects in confined liquid water

An analysis of Rayleigh wing and Raman scattering data performed in water confined in a nanoporous GelSil matrix, is presented. In the restricted translational region, the results show a strong modification of the vibrational dynamics of water in the confined state, with the disappearance of the 60 cm⁻¹ and 170 cm⁻¹ lattice bands in the VDOS. Furthermore, the collective contribution to the polarised OH stretching band comes down indicating that the tetrabonded network is destroyed.     

一种用多色光作为激发源产生拉曼光谱的新算法

探讨用多色光代替激光作为拉曼光源的新型拉曼光谱仪的可能性。根据拉曼光谱原理, 并通过数学分析, 发现当用多色光照射在样品上时, 所得到的散射光经散射频率校正后在不同频率上的强度分布可以写成样品的Raman-Rayleigh联合散射谱和激发光光源的功率谱的卷积。利用傅里叶变换算法,有可能从多色光照射样品所得到的散射光谱中导出样品的拉曼光谱。基于上述原理,可能发展出不用激光的新一代拉曼光谱仪。     

Propagation of transverse hypersound in solution with stratification region

The fine structure of the Rayleigh line wing depolarized spectrum in a form of a triplet caused by the light scattering by transverse hypersonic waves was detected in a critical solution with a closed stratification region at low temperatures. The propagation velocity of transverse hypersound and its absorbance were measured. The temperature dependence of the shear modulus in solution was calculated. The temperature dependence of the shear modulus was compared to temperature dependences of limiting bulk elastic moduli. The results obtained suggest that the solution structure changes in passing through the stratification region at changing temperature.     

Narrow-linewidth passband filter for ultraviolet rotational Raman imaging

We present a narrow-passband spectral filter capable of frequency-resolved imaging of rotational Raman light scattering with strong spectral rejection of out-of-band Raman, Rayleigh, and Mie scattering. The filter is based on mercury-vapor absorption, and subsequent resonant fluorescence and has a passband of less than 1 cm(-1). It is paired with an injection-seeded, cavity-locked, frequency-tripled Ti:sapphire laser that produces >30 mJ/pulse of single-mode, tunable light in the vicinity of 253.7 nm. The laser and filter are combined to spectrally resolve scattering from individual rotational Raman lines of nitrogen and oxygen.     

Direct determination of gas velocity and gas temperature in an atmospheric-pressure argon-hydrogen plasma jet

Direct gas temperature and gas velocity measurements made in the exit plane of a subsonic argon-hydrogen thermal plasma jet from high-resolution lineshape analysis of laser light scattered by the plasma are reported. The lineshapes are in general a superposition of the ion feature of the Thomson-scattered light and the lineshape of Rayleigh scattered light. In the center of the jet Thomson scattering dominates while at larger radii Rayleigh scattering dominates. Because of the complexity of the lineshapes of light scattered by multicomponent plasmas, only those that are predominantly due to Thomson scattering can in practice be analyzed for gas temperature. Gas velocity can be determined from the Doppler shift of the lineshapes relative to the frequency of the incident laser if the velocity is greater than about 50 m s⁻¹. The maximum gas temperature measured was 14,500 K±5%. The maximum gas velocity measured was 1100 m s⁻¹±3%. Temperature values and the radial velocity profile are compared with those previously obtained from a subsonic all-argon plasma jet operated under similar conditions.     

Frequency-dependent polarization of incoherently excited fluorescence

We use detailed-balance considerations to relate the frequency-dependent polarization of atomic fluorescence excited by broad-band radiation to the polarization properties of the collision-induced fluorescence line excited by narrow-band radiation. The polarization of the fluorescence in the first case must display a change when the detected frequency is tuned outside the bandwidth, due to the contribution of Rayleigh scattering. In the special case of adiabatic reorientation followed by emission in the quasistatic wing of the spectral line, we derive explicit expressions for the frequency-dependent polarization in terms of the contributions to the quasistatic profile from the various interatomic difference potentials.     

A comparative performance evaluation of micro-Raman spectrograph using holographic notch filter and dielectric filter

An indigenously designed and developed micro-Raman spectrograph, consisting of a diode-pumped solid-state green laser for the excitation of Raman scattering, a Raman imaging microscope, CCD as a detector and a notch filter, has been extensively studied to evaluate its performance. A dielectric edge filter (having 27 alternate layers of SiO₂ and TiO₂) and a holographic notch filter (Oriel make) have been used to block the Rayleigh scattered light from the sample to the entrance slit of the spectrograph. Holographic notch filter is found to be able to record the Raman shifts below 700 cm⁻¹ conveniently whereas dielectric edge filter (27 layers) has enabled the spectrograph to record the Raman spectra very efficiently after a wave-number shift of 700 cm⁻¹. It has also been observed that the instrument using the edge filter provides a peculiar spectrum consisting of three spectral lines having Raman shifts as 569, 1328 and 1393 cm⁻¹ in the Raman spectrum of a weakly scattering sample with large reflectivity. Similarly, a spectrum consisting of multiple lines has been observed when the instrument is being operated using a holographic notch filter. These spectral lines are not observed in the case of liquid samples such as benzene, carbon tetrachloride, ethanol, diethyl ether etc. The origin of these peculiar spectral lines has been briefly discussed in the paper. Additionally, a major motivation for this work is to utilize the results for the selection of an appropriate filter depending on the type of the sample, i.e. weakly scattered and highly reflecting sample or highly scattered and low reflecting sample.     

基于三级Fabry-Perot标准具的纯转动拉曼测温激光雷达

提出了新的纯转动拉曼测温雷达系统,即以种子激光注入锁定的Nd:YAG激光器为激发光源,采用基于三级Fabry-Perot(F-P)标准具的双通道分光结构代替双光栅单色仪结构.通过通道中宽带滤光片(带宽为7nm)及F-P标准具的组合使用,对532nm激发光的大气Mie-Rayleigh弹性回波散射抑制比可达10^-10,对量子数J=±6,J=±12的N₂纯转动拉曼散射光谱线接收带宽均小于10pm,因此能充分抑制大气背景辐射噪声及O₂纯转动拉曼谱线的干扰,从而实现了单谱线比反演温度,提高了探测精度,且可在白昼探测大气对流层温度.最后通过探空气球测得的对流层温度垂直分布逆向模拟了该系统双通道的Raman信号曲线,证实了该系统的可行性. 关键词： 拉曼激光雷达 纯转动拉曼散射 三级Fabry-Perot标准具 对流层     

光纤背向激光自发喇曼散射的温度效应研究

从理论和实验上研究了光纤背向激光自发喇曼散射的温度效应.光纤背向激光自发反斯托克斯喇曼散射、斯托克斯喇曼散射光的相对强度正比于光纤分子上、下能级粒子数的布居,依赖于温度.由于实际系统中,作为分光用的干涉滤光片不可能完全隔离背向瑞利散射光,因此,实际系统温度曲线比理论曲线低,本文给出了理论修正公式,提出了附加修正项,它与隔离度和波长有关.