Diagnostics of skin pathologies based on spectral analysis of backward and raman scattering

A mathematical model of the interaction of optical radiation with skin tissues is developed taking into account stimulated Raman scattering. Numerical experiments show that the backscattering spectra possess specific features typical of skin pathologies. It is shown that the pathology type can be determined from an analysis of the differential ratios of the Raman scattering intensities at 1271 and 1663 cm^?1 to the intensity in the region of 1454 cm^?1. It is found that the difference in the differential ratios of the Raman scattering intensities for pathologically changed and normal layers may exceed 40%.     

Giant Raman optical activity of the 128-cm-1 mode in α-quartz

The threshold intensity of stimulated Raman scattering along the c-axis in α-quartz was measured for the 128-cm^-1 optical lattice vibration as a function of pump laser polarization at T = 10 K. In a right-handed, optically active quartz crystal the Raman threshold intensity for left-handed, circularly polarized pump light was lower by a factor of about 1.5 than for right-handed, circularly polarized light. The difference in threshold intensity is discussed in terms of Raman optical activity.     

Bimodal dependence of light scattering/fluctuations on the concentration of aqueous solutions

Two concentration ranges (from 10^?5 to 10^?9 and from 10^?13 to 10^?18 M) corresponding to enhanced fluctuations of Rayleigh and Raman scattering of second-harmonic (527 nm) pulses of YVO₄:Nd³⁺ laser are found for aqueous solutions of antioxidant potassium phenosan. A correlation is revealed between the rise in elastic Rayleigh scattering intensity and its fluctuations and the shift of the center of OH Raman band of water toward the ice component characteristic frequency (3200 cm^?1). The development of phase-equilibrium instabilities is analyzed based on the model of fluctuations of the number of hydrogen bonds on the assumption of formation/destruction of ordered hydration layer of phenosan molecules in water.     

Hyper‐Raman and Raman scattering in paratellurite TeO2

Raman spectra of the tetragonal structure of paratellurite TeO₂ have been revisited avoiding anomalous polarization‐selection‐rules violations previously observed and due to optical activity. We present a complementary hyper‐Raman scattering study of paratellurite. Wavenumber and symmetry assignments are given for all expected 21 Raman active optical branches, except one LO component (out of the eight expected TO–LO pairs) of the polar doublet E modes. Also, the four expected hyper‐Raman active A₂ (TO) modes have been observed. Moreover, we have observed a strong Kleinman‐disallowed hyper‐Rayleigh signal, which is tentatively assigned as a first evidence of hyper‐Rayleigh optical activity. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

光纤共振和预共振喇曼光谱

在液芯光纤内产生共振和预共振喇曼效应,喇曼光谱强度可以大幅度提高,最高可达10⁹倍.本文介绍获得光纤(预)共振喇曼光谱的可行性、实验及实验结果.用远离吸收带的激光激发获得了α甲基吡啶预共振喇曼光谱.用小功率激光(0.8mW)、低浓度溶液(9.6×10¹²mol/L)还获得了β叶红素在CS₂中的共振喇曼光谱.     

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.     

Studies of relaxation times of secondary radiations in ZnTe by circular polarization correlation

Population and spin relaxation rates concerned with exciton luminescence and multiple LO-phonon emission lines are studied in ZnTe at 77 K by means of optical circular polarization correlation between the exciting and emitted lights. The decay times of the LO lines are determined to be much less than 10^-11sec, which are definitely shorter than the obtained exciton lifetime of 10^-10-10^-9sec. It is concluded that the LO lines are not due to hot luminescence but due to resonance Raman scattering.     

多道激光Raman光谱检测系统

设计了一种多道激光Ｒａｍａｎ光谱检测系统,由Ａｒ＾＋激光器、外光路、多色仪和光学多道分析仪（ＯＭＡⅡ）组成,通过对ＣＣｌ４、Ｃ６Ｈ６、Ｃ６Ｈ１２的Ｒａｍａｎ光谱的检测表明,与单道激光Ｒａｍａｎ光谱检测系统相比,多道系统大大缩短记录Ｒａｍａｎ光谱的时间,但每道的积分时间可延长至１０－５０ｓ,将多道探测器的工作温度降低到５℃,可获得信噪比高、灵敏度高、质量好的Ｒａｍａｎ光谱。采用微分软件处理Ｒａｍａｎ     

Investigation of micropipes in 6H-SiC by Raman scattering

The spectra of 6H-SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796 cm⁻¹ is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations.     

光纤维中的喇曼混频

我们在656厘米^-1到1343厘米^-1的频率范围研究了光纤维的调谐喇曼混频(RM)效应。在实验中观察到下列现象:相干反斯托克斯喇曼散射(CARS)的大小与逆喇曼吸收(VRA)的大小成反比;RM对受激喇曼散射(SRS)的强度分布有强烈影响。除了观测到相干斯托克斯(CSRS)和CARS辐射,还观测到二级相干斯托克斯(SOCSRS)和相干反斯托克斯(SOCARS)辐射。对实验结果进行了讨论。 关键词：     

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

Rayleigh backscatter noise in integrated optical resonance gyro

Rayleigh backscatter noise in integrated optical resonance gyroscope (IORG) is researched both in theoretically and experimentally. The characteristics of Rayleigh backscatter noise in the resonator of SiO₂ on Si substrate are formulized, and the static state and dynamic state models of IORG are constructed. The relationship between the optical signal and Rayleigh backscatter noise is simulated, and the affection between the interference signal of Rayleigh backscatter noise and reverse optical signal is also calculated. The degree of degrading the performance of resonator due to Rayleigh backscatter noise is analyzed, such as finesse and fundamental detection limit. The relationship between the line-width of the tunable laser and the intensity of transmit light and Rayleigh backscatter noise is simulated. Through the theory of modulation, the method of inflicting two different frequencies to the arm of integrated optical modulator is presented. The verified experiment result showed that the saw-tooth wave modulation could effectively restrain Rayleigh backscatter noise in IORG.     

Incident circularly polarized Raman optical activity spectrometer based on circularity conversion method

A simple incident circular polarization Raman optical activity (ICP ROA) spectrometer was constructed by applying the method of circularity conversion. The circular polarization of the incident laser light was modulated between right and left by the insertion of a half‐wave plate and not by using a Pockels cell which is usually used in ICP ROA instruments. On the basis of the concept of the virtual enantiomer (Hug, W. Applied Spectroscopy, 2003, 57, 1), circularity converters were inserted in the optical train, which could effectively compensate the systematic offset. The new instrument successfully attained photon shot‐noise‐limited conditions for all bands except for the very strongly polarized Raman band. The ROA spectra of some standard chiral samples were measured to demonstrate the performance of the spectrometer. Copyright © 2010 John Wiley & Sons, Ltd.     

Polarisation dependent Raman study of single-crystal nickel oxide

The magnetic domain structure and Raman scattering have been studied in NiO single-crystals with three different (100), (110) and (111) orientations. Twin-domain structure was observed in NiO(100) and NiO(110) single-crystals using cross-polarized optical microscopy. We found that the ratio of the two-magnon (at 1500 cm⁻¹) to the two-phonon (2LO, at 1100 cm⁻¹) Raman bands intensity is sensitive in a particular way to the type of the twin-domain pattern.     

Upconversion luminescence of Tm/Yb-codoped oxyhalide tellurite glasses

Thermal stability, Raman spectra and blue upconversion luminescence properties of Tm³⁺/Yb³⁺-codoped halide modified tellurite glasses have been studied. The results showed that the mixed halide modified tellurite glass (TFCB) has the best thermal stability, the lowest phonon energies and the strongest upconversion emissions. The effect of halide on upconversion intensity is observed and discussed and possible upconversion mechanisms are evaluated. The intense blue upconversion luminescence of Tm³⁺ in TFCB glass may be a potentially useful material for developing upconversion optical devices.     

多波长消荧光拉曼光谱仪的研制及应用研究

拉曼光谱技术作为探究分子、晶体及其结构特征的有力手段,具有快速、无损、样品用量小、无需前处理且适应性强等优点,已被广泛应用于食品安全、石油化工等领域。但在拉曼光谱应用中,常常受到荧光背景干扰,导致拉曼信号降低,严重的情况下拉曼信号甚至会淹没在荧光背景中。为解决拉曼技术在实际应用中荧光背景干扰的问题,从仪器角度出发,采用二色镜对多波长拉曼光谱进行光路耦合设计,研制了近红外拉曼光谱与移频差分拉曼复合一体的多波长消荧光拉曼光谱检测系统,其中近红外拉曼光谱采用1 064 nm激光光源设计,移频差分拉曼光谱选取784.5和785.5 nm两组激光光源进行时分复用,在移频差分拉曼光谱检测的同时,亦可获得两组单波长拉曼光谱数据。通过对比同步测试和分时逐次测试的强度及峰位稳定性,验证了多波长消荧光拉曼光谱仪的同步测试性能;选取了多种荧光背景强弱不同的样品,进行了单波长拉曼、近红外拉曼及移频差分拉曼光谱的对比分析。针对丙酮、乙腈等荧光背景较弱的样品,可采用单波长拉曼光谱对样品进行定量及定性分析;针对食用油、红色塑胶微粒等荧光背景与拉曼信号强度相当的样品,可采用近红外拉曼光谱对样品进行定量及定性分析;针对红酒、棕色塑胶微粒等荧光背景较强的样品,需结合近红外拉曼光谱和差分拉曼光谱对样品进行定性分析。研究表明：通过多波长消荧光拉曼光谱检测系统的研制,在常规单波长拉曼光谱技术的基础上,将两种抑制荧光干扰技术有机结合,有效扩充了应用领域及样品检测范围。     

Surface enhanced Raman scattering of light by ZnO nanostructures

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E ₂(high) and A ₁(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10³) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.     

Dynamics of cascaded Brillouin-Rayleigh scattering in a distributed fiber Raman amplifier

We investigate the dynamics of a novel multiwavelength generator in which cascaded-stimulated Brillouin scattering and Rayleigh scattering are automatically balanced to given an evenly spaced (9.4-GHz), highly flattened (<3-dB) optical frequency comb over a 57.2-nm span. The extended effective length for the relevant nonlinear processes from the distributed Raman gain and the reduced Brillouin threshold from the seeding effect of Rayleigh backscattered waves are considered to be the key factors that explain the operation of this structure.