Resonant stokes and anti-stokes Raman scattering of light in CdSe/ZnSe nanostructures

Raman scattering spectra of CdSe/ZnSe multilayer nanostructures with a CdSe insert of a nominal thickness of 2.1 monolayers were studied. A heavy dependence of the intensity and of the frequency position of the multiphonon Stokes and anti-Stokes LO bands on the exciting photon energy was detected. The results obtained are interpreted as a resonance with various exciton transitions in the CdSe insert and barrier ZnSe layers. A difference between the Stokes and anti-Stokes frequencies of LO bands observed as the resonance conditions are varied confirms the inhomogeneous nature of the photoluminescence band of CdSe quantum dots.     

Coherent anti-Stokes Raman scattering and normal anti-Stokes Raman scattering due to LO phonons in GaP using cw diode lasers

Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm⁻¹ LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were <20 and 50 mW, respectively. The diameter of the laser beams in the focal plane of the focusing lens was determined to 40±5 μm. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were <2 and 5 kW cm², respectively. The powers of the CARS and NARS signals were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm⁻¹, using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions.     

Influence of the scattering matrix elements on the gain of Stokes and anti-Stokes components in the nonstationary regime

The influence of the scattering matrix elements that are responsible for the amplification of the Stokes and anti-Stokes components on the process of stimulated Raman scattering in the essentially nonstationary regime is analyzed. It is demonstrated that the optimum proportion between the scattering matrix elements, which maximizes the anti-Stokes component, is determined by the ratio between the optical frequencies of the components and the initial proportion between the intensities of the pump and initiating pulses. In the case of the optimum proportion between the scattering matrix elements, the variation in the excitation of a medium compensates the self-induced modulation of gain, and the efficiency of converting the radiation energy into the Stokes and anti-Stokes components increases substantially.     

单模双折射色散缓变光纤中拉曼散射与参量放大

根据斯托克斯波和反斯托克斯波所满足的耦合微分方程,考虑泵浦波是线偏振光,其偏振方向沿x轴,推导出了同偏振方向受激拉曼散射和参量放大同时作用下,斯托克斯波和反斯托克斯波的增益系数。研究了色散缓变光纤中增益随失配系数Δk2以及归一化距离z/L的变化关系。结果表明,当非线性系数γ=0时,增益随Δk2的变化情况在正常和反常色散区是完全对称的;而当非线性系数γ≠0时,在反常色散区增益会出现峰值,随后增益随Δk2和z/L的增加而逐渐减小。讨论了反斯托克斯波与斯托克斯波Eax/Esx的比值随失配系数Δk2的增加而快速衰减的变化特性。     

Generation of anti-Stokes radiation upon amplification of stokes pulses in transient stimulated Raman scattering

An analytical solution is obtained for equations of transient stimulated Raman scattering for short samples and a weak seed Stokes wave in the approximation of a given pump field, and a numerical solution for more extended media or more intense input Stokes pulses with allowance for pump depletion. The dependence of the anti-Stokes wave energy on its spatial mismatch with the Stokes and laser waves is studied. The optimum angle of the anti-Stokes generation is found as a function of the length of the system, transverse relaxation rate, laser pulse energy, and intensity ratio of the Stokes and pump pulses at the entrance of the sample.     

Introduction to Terahertz Raman spectroscopy

This work, intended for advanced undergraduate students, explains the basic concepts and an actual scientific use of Terahertz Raman spectroscopy, displaying some of the benefits of this versatile technique for structural analysis of molecules building up materials since this technique has been increasingly used for molecular characterization in chemistry. A good didactic example of the experimentally applied temperature dependence of molecular vibrations according to the Boltzmann distribution is the ratio of anti-Stokes to Stokes Raman peak intensity used to calculate the temperature of a nylon 6,6 sample. The comparison of the temperature of nylon 6,6 calculated from the experimentally determined anti-Stokes to Stokes peak intensity ratio in the Terahertz region with the temperature set with the help of a heating-freezing stage is discussed. The limitations of Terahertz Raman spectroscopy are also part of this fundamental discussion.     

Improved anti-Stokes energy transfer between rare earth ions in Er（0.5）Yb（9.5）：FOV oxyfluoride vitroceramics explains the strong color reversal

The widely used energy transfer theory is a foundation of luminescence,in which the rates of Stokes and antiStokes processes have the same calculation formula.An improvement on the anti-Stokes energy transfer to explain the fluorescence intensity reversal between the red and green fluorescence of Er(0.5)Yb(9.5):FOV is reported in the present article.The range of the intensity reversal Σ was measured to be 877.Dynamic processes for 16 levels were simulated.A coefficient,the improvement factor of the intensity ratio of Stokes to anti-Stokes processes in quantum Raman theory compared to classical Raman theory,is introduced to successfully describe the anti-Stokes energy transfer.A new method to calculate the distance between the rare earth ions,which is critical for the energy transfer calculation,is proposed.The validity of these important improvements is also proved by experiment.     

Noise correlations in a doubly-resonant atomic optical parametric oscillator

The simultaneous generations of bright Stokes and anti-Stokes fields are realized by using only one pump field in a Doppler-broadened atomic medium confined in an optical ring cavity. A vacuum-induced absorption phenomenon is also observed in such a system. By utilizing an external Fabry-Perot cavity to separate the Stokes and anti-Stokes fields, we investigate the noise correlation and anticorrelation properties between the Stokes, anti-Stokes, and the pump fields.     

SRS generation of anti-Stokes radiation under phase quasi-matching conditions

New methods of generation of anti-Stokes radiation of stimulated Raman scattering in media with changeable parameters of the third-order nonlinearity χ⁽³⁾ along the longitudinal coordinate are proposed. The conditions of obtaining phase quasi-matching in different media and reaching the maximum efficiency of conversion into the anti-Stokes component of stimulated scattering are determined by numerical methods. The dependence of the efficiency of energy transfer from the pump wave to the anti-Stokes wave on the ratio of intensities of the pump and Stokes waves at the input of the medium is studied. The models of the media in which the efficiency of generation of anti-Stokes radiation exceeds 30% are obtained. The results of the investigation can be used for the development of new efficient nonlinear optical devices upconverting the laser radiation frequency.     

Linewise Raman-Stokes/anti-Stokes temperature measurements in flames using an unintensified charge-coupled device

One-dimensional, spatially resolved (linewise), temporally averaged Stokes/anti-Stokes temperature measurements with 200 m spatial resolution and 6% precision uncertainty are demonstrated in an opposed-jet-diffusion flame of air vs N₂-diluted H₂ using the Raman-Stokes/anti-Stokes technique. The Stokes/anti-Stokes temperature profile is compared to temperature measurements obtained using all major species'Q-branches and differences between the two sets of results are discussed. In addition, single-pulse, linewise measurements with 710 m spatial resolution and 19% precision uncertainty are also demonstrated. To the authors' knowledge this is the first report of linewise Stokes/anti-Stokes temperature measurements in flames. Simultaneous measurements of the N₂ Stokes and anti-Stokes vibrationalQ-branches are obtained by using an unintensified Charge-Coupled Device (CCD) that is gated by a ferro-electric liquid crystal light valve and/or a low duty cycle optical chopper to suppress detected flame luminosity. This detection system provides increased detection efficiency, dynamic range, and imaged spectral range over an intensified CCD, allowing spatially resolved Stokes and anti-Stokes signals to be imaged onto one detector.     

斯托克斯和反斯托克斯拉曼位移差与时间反演对称性

首先列出若干Stokes和anti-Stokes位移不对称的事例,并在此基础上指出,如果将anti-Stokes散射严格定义为Stokes散射的时间反演行为,则对于初态或末态具有Kramers简并的体系,Stokes和anti-Stokes散射的拉曼位移可以不同.这是因为时间的正过程和反演过程各对应于不同的跃迁途径,其位移大小的差别与简并能级的分裂值相关.     

Cooperative scattering effect between Stokes and anti-Stokes field stimulated by a stream of atoms

This paper is devoted to the study of the cooperative two-photon scattering processes between two resonator modes stimulated by an excited atomic beam. It has been proved that these collective scattering phenomena between the Stokes and anti-Stokes resonator modes are taking place due to the energy transfer between these fields. The statistical properties of the Stokes and anti-Stokes photons have been described using the photon correlation functions. The numerical solution of this equation describes the statistical transformation of n-Stokes photons into anti-Stokes photons.     

The use of diode array detectors in conjunction with continuous wave gas lasers for anti-Stokes Raman spectroscopy

The Raman spectrum of any molecule consists of two mirror-image signals, th e Stokes and anti-Stokes Raman spectra. In most cases, unless highly specific sampling conditions are used, the anti-Stokes signal is much weaker than that of the Stokes. The recent application of intensified diode array detectors to Raman spectroscopy has produced a marked increase in the sensitivity of the technique which makes a study of the anti-Stokes spectrum potentially more rewarding than it has been to date. The present study has shown that, although of limited use for general purposes, there are some specific instances where the anti-Stokes spectrum can be of considerable practical use. Such applications are to extend the operating range of the Raman spectrometer, to study photodegradable samples and for the analysis of samples which exhibit strong fluorescence.     

Raman光激射器

本文从哈密顿量出发,导出描写受激Raman过程的方程式:Laser光、一级Stokes与反Stokes光及相干的声子场的耦合方程,并唯象地引入弛豫耗散。在分子属于远共振情形及比介电常数近似更高一级的近似下,分析了方程的性质。由平衡点稳定性的讨论给出了Raman光激射器的阈值,发现反Stokes激射光的产生并不要求附加的阈条件,即在受激Raman效应中,反Stokes光总是必然出现的。对于Raman光激射器诸工作点的性质及工作过程也作了进一步的讨论,发现在一定条件下,在强激射光源辐照下,存在着Stokes与反Stokes成分几乎各占一半的唯一的稳定平衡点(Raman光激射器的工作点)。文中也顺便讨论了声子弛豫所起的作用及有长寿命的声子时Raman光激射器的行为。     

Raman spectroscopic evidence for hot-phonon generation in electrically biased carbon nanotubes

We provide spectroscopic evidence for hot-phonon generation in biased single-walled carbon nanotubes by measuring simultaneously the Stokes and anti-Stokes Raman lines of the G mode and of the radial-breathing mode as a function of current bias. Using Bose-Einstein statistics we can directly calculate the phonon temperature from the intensity ratio of the anti-Stokes to Stokes lines. Upon nanotube biasing we observe (i) an increase of the G mode phonon temperature in contrast to the radial-breathing mode phonons that remain thermalized at room temperature, and (ii) no softening of the G mode. Based on these observations, we exclude current-induced thermal heating of the nanotube.     

Anti-stokes fluorescence of polymethine dyes excited by a titanium-sapphire laser

Fluorescence of symmetric polymethine dye solutions (λ _abs ^max ≈ 700 nm) upon anti-Stokes excitation by cw radiation of a titanium-sapphire laser (781 nm) is first investigated. A series of six compounds with analogous composition and spectral and luminescent properties is investigated. It is demonstrated that in addition to the anti-Stokes component, the Stokes component with a maximum at 820 nm (referred to the H-aggregates of initial dyes) is observed in the fluorescence spectra of solutions of the examined molecules when dye concentration increases to 10⁻³ M. Dependences of the anti-Stokes and Stokes component intensities on the exciting radiation power are obtained that confirm a linear excitation character. On examples of xanthene and polymethine dyes, the use of organic fluorophors for anti-Stokes laser cooling and some other possible applications of the anti-Stokes fluorescence are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 63–70, March, 2007.     

在单模光纤中放大的反斯托克斯拉曼背向自发散射的温度效应

在单模光纤中,输入的激光功率大于阈值时．出现放大的反斯托克斯拉曼背向自发散射现象。实验发现：放大的反斯托克斯拉曼背向自发散射具有温度效应．与反斯托克斯拉曼背向自发散射一样,放大的拉曼散射光的光子通量受到光纤温度的调制。反斯托克斯拉曼背向白发散射的放大效应抑制了单模光纤中的相干噪声,改善了系统的信噪比。实验还发现．放大的反斯托克斯扎曼背向自发散射空域曲线上放大的端点位置随激发功率的增高前移并具有一定的规律性。放大的反斯托克斯拉曼背向自发散射的温度效应作为一种新的测温原理,已应用于远程30km分布光纤温度传感器系统。     

High-spectral-resolution coherent anti-Stokes Raman scattering with interferometrically detected broadband chirped pulses

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.