High enhancement factor of Au nano triangular prism structure for surface enhanced coherent anti-Stokes Raman scattering

Coherent anti-Stokes Raman scattering spectroscopy(CARS) is a well-known detecting tool in biosensing and nonlinear spectroscopy. It can provide a non-invasive alternative without the need for exogenous labels, while the enhancement factor for surface plasmon resonances(SPR) are extensively used to increase the local field close to the oscillators and which can obtain high enhancement. In this work, we investigate the enhancement factor of our structure for surface-enhanced coherent anti-Stokes Raman scattering. The absorption spectrum of the structure has been studied, a wide range of absorption has been realized. The enhancement can be as high as 10¹⁶ over standard CARS. Our design is very useful for improving the enhancement factor of surface-enhanced coherent anti-Stokes Raman scattering.     

Stokes-Anti-Stokes Iterative Resonator Method for Modeling Raman Lasers

We present a novel modeling method to describe the steady-state and transient regimes of a continuous-wave pumped Raman laser emitting both Stokes and anti-Stokes photons. Our so-called "Stokes-anti-Stokes iterative resonator method" evaluates for every half round-trip time the longitudinal distribution of the intracavity pump, Stokes and anti-Stokes fields propagating in forward and backward directions. Although this Stokes-anti-Stokes iterative resonator method is widely applicable, its most important asset resides in its ability to accurately model Raman lasers that feature cavity enhancement of the pump power and that emit both Stokes and anti-Stokes photons. Important here is that our modeling method correctly incorporates the longitudinal intracavity field distributions, the generation of anti-Stokes photons, and the interference effects between incident and intracavity pump fields, and that it describes not only the lasers' steady-state operation but also their transient characteristics. We demonstrate for both a hydrogen-based and a silicon-based Raman laser with pump cavity enhancement that the Stokes-anti-Stokes iterative resonator method performs better than the modeling methods presently used for these categories of Raman lasers. Finally, to demonstrate the potentialities of our modeling method, we numerically simulate, for the first time according to our knowledge, the anti-Stokes emission generated by a silicon-based Raman laser     

CARS显微术的基本原理及其进展

相干反斯托克斯拉曼散射(CARS)以其散射强度高、方向性好、背景干扰小等优点成为分子研究的有力工具,CARS显微镜不仅可以对样品进行光谱研究,还可以对其进行功能性成像．提高了分子分析的信息量。介绍了CARS显微术的理论结果、不同结构及其在生物学领域的应用等。     

Coherent Raman gain spectroscopy using CW laser sources

The recent demonstration of stimulated Raman gain (loss) spectroscopy (SRS) using CW laser sources introduces a powerful tool to coherent Raman spectroscopy. In this paper we undertake an experimental and analytical evaluation of several variations of SRS using CW laser sources including (1) direct stimulated Raman gain (loss) measurements, (2) optically heterodyned polarization interferometry, and (3) two-beam nonlinear interferometry. The results show CW SRS to be a convenient and effective means of obtaining direct Raman spectra in applications where background fluorescence precludes the use of conventional Raman techniques. Sensitivities comparable to or exceeding those obtained by coherent anti-Stokes Raman spectroscopy (CARS) are demonstrated. Ultimate sensitivities exceeding those achieved by spontaneous Raman spectroscopy are expected for high-resolution applications in gaseous media.     

甲醇溶液相干反斯托克斯拉曼光谱(CARS)的选择激发

利用飞秒自适应脉冲整形相干控制技术成功实现了甲醇溶液中甲基对称(vS(CH3)2832cm-1)和反对称(VAS(CH3)2948cm-1)振动能级相干反斯托克斯拉曼光谱(CARS)的选择激发.为了进一步探究双光束飞秒CARS光谱实现选择激发的机制,采用二次谐波频率分辨光学开关(SHG-FROG)测量方法对整形前后的泵浦激光脉冲进行了探测. SHG-FROG痕迹结果显示裁剪泵浦光中的有效频段可实现飞秒CARS的选择激发.研究表明飞秒自适应脉冲整形相干控制技术对于复杂分子系统飞秒CARS的选择激发研究具有非常重要的科学意义.     

时间分辨相干反斯托克斯拉曼散射显微成像技术中光的干涉

时间分辨相干反斯托克斯拉曼散射显微成像技术中的泵浦光和探测光采用同一波长,可以很大程度上降低成像系统对光源的要求.采用振幅矢量叠加法理论上计算了波长相同的两束光经由物镜产生的双光束干涉,分析了产生的CARS信号强度波动的原因,并提出通过调整泵浦光与探测光的偏振方向相互垂直的方案消除干涉项,这样可以实现时间分辨CARS消除非共振背景的同时,保证产生的信号稳定.     

CARS thermometry of polyatomic gases: SF6

Coherent anti-Stokes Raman spectroscopy (CARS) has been used to study the temperature behavior of SF6gas. In the temperature range 200-1000 K, evaluation of CARS bandwidths and lineshifts resuited in a relatively precise temperature determination. The advantages of a CARS-based SF6thermometer are discussed in detail.     

氮气CARS理论光谱计算及在温度测量中的应用

基于量子理论,对相干反斯托克斯拉曼散射(CARS)的机理进行了探讨,给出了氮气分子Q支CARS光谱的理论计算模型。进行了氮气分子拉曼散射截面、不同能级分子布居数密度差、振转配分函数及三阶非线性极化率的计算。仿真结果表明适当的简化能够大大缩短光谱计算的时间,并且与已有的结果比较接近,能够应用于CARS测量应用。介绍了能够用于瞬态温度场测量的单脉冲CARS装置,理论光谱分辨率可达0.1cm-1,轴向空间分辨率5mm,光谱采样频率10Hz。     

Up-conversion of excimer lasers via stimulated anti-Stokes Raman scattering

Up-conversion schemes for various excimer laser systems based upon anti-Stokes Raman laser action are proposed. Four atomic systems, TI, In, I, and Br, are considered as host media for the Raman laser up-converter. Gain calculations indicate that anti-Stokes Raman up-converters should permit a variety of new tunable laser sources in the 150-325 nm spectral region.     

Stimulated Raman Scattering in Nanorod Silicon Carbide Films

When the film is excited by a very low excitation energy, the spontaneous Raman scattering emerges. The intensity of Raman scattering is proportional to the excitation power below the threshold excitation. When the excited power reaches the excitation threshold, the intensity of Stokes light strongly increases. Meanwhile an anti Stokes light at 495 nm and multiple order but small Stokes peaks occur. The intensity of Stokes light is much larger than that of anti Stokes. The full width of half maximum (FWHM) of Stokes peak is reduced from 0.4 nm to less than 0.2 nm, the scattering angle between both Stokes and incident lights becomes less than 1°, and the angle between the Stokes and anti Stokes lights is about 3°. When the exciting power is in excess of the threshold, anti Stokes and multiple Raman scattering peaks reappear. These experiments can be unlimitedly repeated. From this experiment, we can exclude the possibility of spontaneous Raman scattering. It is suggested that the nanorods are a quantum line dimension having a large surface. There will be Raman differential scattering section so long as the nanorod films become very strong scattering media; the surface enhanced Raman scattering will be produced, the nanorod films of SiC will form a strong multiple scattering resonance cavities so as to form the stimulated Raman scattering oscillation.     

VUV generation by high-order CARS

Generation of VUV (vacuum ultraviolet) radiation by stimulated Raman scattering (SRS) in H₂ is studied with collinear irradiation of the first Stokes component simultaneously with pump laser radiation. Improvements of the high-order coherent anti-Stokes Raman scattering (CARS) method over the pure SRS scheme are: generation of higher anti-Stokes (AS) orders, increased conversion efficiency, and considerably better reproducibility. Experimental results are presented to confirm the theoretical analysis     

斯托克斯光种子法固体相干反斯托克斯拉曼频移器的理论研究

以波动方程和受激拉曼散射(SRS)物质方程为基础,采用光种子法,建立了固体相干反斯托克斯拉曼频移器的归一化耦合波方程,研究了晶体中反斯托克斯光转换效率。在脉冲抽运条件下分析了归一化增益系数G、归一化相位失配系数ΔK以及一阶斯托克斯光种子的归一化光场振幅ψs0三个变量对固体相干反斯托克斯拉曼频移器的影响,并作出了一系列相应曲线,由所得曲线估算了各归一化变量的合理取值范围。分析结果表明,在ΔK=0时,通过增大sψ0来打破拉曼增益抑制的影响,其转换效率峰值可达到44%。而当sψ0较弱时,可选取合适的相位失配系数,反斯托克斯光转换效率可达40%。     

In-Situ mechanistic studies of the reaction of trimethylgallium and phosphine in zeolite H-Y

Coherent anti-Stokes Raman scattering (CARS) has been utilised to monitor the decomposition of trimethylgallium (TMGa) on the reactive internal surface of the protonated form of zeolite Y under metal organic chemical vapour deposition (MOCVD) conditions designed to produce GaP deposits that exhibit quantum-size effects. The CARS data clearly reveal the facile room temperature decomposition of TMGa in the zeolite, as evidenced by the detection of increasing levels of methane with increasing reaction time. In addition, the zeolite samples were analysed by solid state nuclear magnetic resonance with magic angle spinning (MAS NMR) before reaction, after reaction of TMGa and after subsequent reaction with phosphine at 300°C. These data reveal that TMGa reacts with acid sites in the zeolite 12-rings, resulting in species containing methyl groups. Subsequent exposure to phosphine removes these methyl group protons, leaving various, as yet not fully characterised, phosphorus species. Exposure to phosphine does not appear to regenerate the acid sites on the zeolite.     

反斯托克斯拉曼转换增益系数的最佳化

研究了反斯托克斯拉曼转换与受激拉曼散射之间的竞争过程，讨论了反斯托克斯拉曼转换增益系数的最佳化。     

光纤拉曼散射效应及其应用研究

测量了G652光纤和DCF光纤的背向散射光谱，在斯托克斯区观察到一级和二级拉曼背向散射光谱，在反斯托克区观察到一级拉曼背向散射光谱，首次在斯托克斯区和反斯托克区观察到ZX背向散光谱。光纤背向散射效率直接应用于光纤拉曼放大器和分布式光纤拉曼温度传感器系统。讨论了分布式光纤拉曼温度传感器系统工作原理、结构，给出了实验结果。     

苯的二级相干反斯托克斯喇曼散射(CARS)

设计了一套光路布置使用受激喇曼散射为相干光源,泵浦光子同受激光子之间混频,观测到苯的相干反斯托克斯喇曼散射共振现象,并获得很强的第二级相干反斯托克斯喇曼线.     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

Raman amplifier model in single-mode optical fiber

Equations to describe the process of Raman amplification in single-mode optical fiber and Stokes and anti-Stokes spontaneous emission generation with conservation of photon number are derived from first principles. The numerical simulation of Stokes and anti-Stokes spontaneous emission is in good agreement with experimental results. The importance of the sometimes-omitted anti-Stokes spontaneous emission terms in wavelength-division-multiplexed situations for optical signal-to-noise ratio is demonstrated by the simulation of light propagation through transmission fiber with and without Raman amplification.     

Exact and approximate expressions for χ(3) in CARS diagnostics measurements

Coherent anti-Stokes Raman scattering (CARS) is a useful tool in combustion diagnostics. In such experiments, the measured spectrum is compared to the predicted one and information is obtained about species temperature and concentration. We examine conditions for the validity of approximate expressions for the nonlinear susceptibilitychi^{(3)}and indicate the importance of using the full expression in the general case, especially near one photon resonance, or under conditions of high pressure.     

内腔泵浦的BaWO4反斯托克斯拉曼激光器实验研究

实验研究了内腔BaWO4反斯托克斯拉曼激光器的激光特性。通过在调Q的基频谐振腔中插入一倾斜的BaWO4拉曼谐振腔,实现基频光、一阶斯托克斯光和一阶反斯托克斯光的非共线相位匹配,进而实现了内腔反斯托克斯拉曼激光器在968nm的运转。测量了不同泵浦电压下输出的一阶反斯托克斯光的单脉冲能量,当泵浦电压为750V时,获得的最大输出能量为0.79mJ,相应的基频光到一阶反斯托克斯光的转化效率为1.5%。一阶反斯托克斯光的典型脉冲宽度为4.9ns。