Raman response function and Raman fraction of phosphosilicate fibers

The Raman response function and Raman nonlinear index of phosphosilicate fibers are calculated for several P₂O₅ concentrations. The nonlinear index of phosphosilicate fiber is estimated by using the Boling formula, and it is used to calculate the Raman fraction of the nonlinear index. On the other hand, the Raman response function of the phosphosilicate fibers is fitted to a superposition of six phase-shifted under-damped functions in order to use it in the numerical simulation of ultra-short pulse propagation. We show through numerical simulations that phosphosilicate fibers are a suitable medium to observe a scaling up of the Raman self-frequency shift when compared to silica fibers.     

Raman response function for silica fibers

The commonly used Lorentzian form of the Raman response function for studying propagation of ultrashort pulses in silica fibers does not properly account for the shoulder in the Raman gain spectrum originating from the Boson peak. We propose a more accurate form of this response function and show that its predictions for the Raman-induced frequency shift should be in better agreement with experiments.     

共焦腔增强的空气拉曼散射

拉曼光谱是一种无损、快速的物质成分分析和检测方法.由于拉曼信号强度微弱,使得拉曼光谱的检测应用受到极大的限制.针对增强拉曼散射信号强度、提高检测灵敏度这一问题,设计了一种用于自发拉曼散射信号增强的共焦腔样品池,开展了基于该共焦腔的空气拉曼散射信号增强研究.共焦腔的腔镜反射率为92%,这一设计在保证共焦腔通带宽度与激光器线宽匹配的同时能有效地降低共振调节难度.实验中采用0°探测构型收集拉曼信号,并由成像式拉曼光谱仪获取光谱信号.实验发现,在共振状态下,共焦腔的耦合效率达到87.5%,单向激光功率实现约11倍放大;与无共振腔相比,共焦腔对拉曼信号实现17倍放大,信噪比提高2倍.此外,空气中CO_2的3σ检测限达到200 ppm量级.结果表明,该系统对自发拉曼散射信号增强效果显著,并且有较高的检测灵敏度.     

探测大气中CO2的Raman激光雷达

基于大气激光后向散射光谱,研究和设计了探测大气CO2浓度的Raman激光雷达,其发射机采用Nd:YAG激光的三倍频354.7nm作为工作波长,发射的单脉冲能量350mJ,重复频率20Hz;接收机采用了光电倍增管(量子效率25%)和光子计数器(计数速率200MHz),探测CO2的Raman散射371.66nm(频移1285cm-1信号,(1小时累加)近地面2.5km以内信噪比不小于8.采用组合滤光片来抑制强的354.7nm Mie-Rayleigh后向散射和氧气375.4nm Raman后向散射对信号的严重干扰.比较分别来自大气CO2和参考气体N2的Raman后向散射回波,可反演出大气中CO2的相对浓度.     

非线性拉曼激光雷达系统检测CO2气体的受激拉曼过程

 利用气体的受激拉曼散射增益效应的非线性雷达技术是探测大气中的CO₂气体的重要方法，用Nd:YAG固体激光器（1 064 nm）的三倍频光（354.7 nm）注入装有CO₂和N₂高压气体的拉曼管中，气体的受激拉曼散射（SRS）过程产生两种气体的一阶斯托克斯光，用来作为拉曼雷达的发射种子光源。介绍了产生光源的实验装置，论述了SRS中气体气压变化与一阶斯托克斯光能量输出变化的定量关系，得到最佳能量输出的优化条件，并对SRS中一阶斯托克斯光产生过程的物理机制进行了讨论。并根据光源的试验结果，设计了非线性受激拉曼雷达系统，对前期的普通拉曼雷达进行了实验，得到了初步的实验结果。     

�����н�����-�����ѹ�Թ�ŵ�

空气中的大气压辉光放电通常因放电易过渡到火花状态而难以产生。在静态大气压空气针-板等离子体发生器中，采用阻容耦合负反馈方法控制等离子体放电发展过程，成功地抑制了辉光放电向火花放电的过渡，产生了稳定的交流辉光放电。研究了电压、电极间距等参数变化对放电的影响。     

空气中大气压下均匀辉光放电的可能性

利用介质阻挡电极结构,对101325×105Pa气压下空气间隙中的放电进行了实验研究,数值模拟计算了实验条件下电子雪崩的发展过程.结果表明:对于长度不大于2mm的空气间隙,可能实现辉光放电.对于长度不小于5mm的空气间隙,如果不能设法降低放电场强,放电必然是流注形式,不可能实现辉光放电.另外,实验结果未能验证“离子捕获”机理降低放电场强而实现辉光放电的正确性 关键词： 大气压辉光放电 电子雪崩 流注     

Temporal gas temperature of atmospheric pressure air plasma

In this paper, temporal gas temperature in plasma was measured by Rayleigh scattering in a passive way since synchronization was difficult due to the randomness of current pulses. The plasma was generated between a 10 mm pin-to-plane gap connected to a H.V DC voltage through a 130 MΩ resistor and a skin sample was placed on a grounded plate. Even the plasma can be touched by a human hand without any feeling of warmth, the peak temperature could be 337 K then decrease to 295 K over 60 μs at 1 mm. Moreover, the applied voltage dramatically affects peak current and the peak temperature. Therefore, the transient “high” temperature cannot be touched and the so-called “cold” plasma might not be “cold”.     

绝对探测大气温度的纯转动拉曼激光雷达系统

纯转动拉曼激光雷达是探测大气温度廓线的重要手段之一,其正常工作需要配置其他并行校正设备,制约其在气象及环境监测领域中的实用化进程.基于大气氮气分子的纯转动拉曼谱型对温度的依赖性,提出并设计了绝对探测大气温度廓线的纯转动拉曼激光雷达系统.系统采用波长532 nm且脉冲能量300 m J的激光激励源和口径250 mm卡塞格林望远镜的接收器,设计了衍射光栅和光纤Bragg光栅结合的多通道并行纯转动拉曼光谱分光系统;仿真分析氮气和氧气分子的纯转动拉曼散射谱线间关系,优化选择了6条氮气分子的纯转动拉曼谱线以直接反演大气温度,设计了两级滤光器间转接光纤阵列的结构;基于最小二乘原理推导了绝对探测大气温度的反演算法,并结合标准大气模型,分析了纯转动拉曼激光雷达绝对探测大气温度的探测性能.结果表明,所设计纯转动拉曼激光雷达系统可直接反演大气温度廓线,在测量时间17 min内,温度偏差小于0.5 K的探测高度达2.0 km.     

Pulsed laser deposition of hard coatings in atmospheric air

A new laser plasma technique for non-vacuum deposition of thin films has been proposed and experimentally realized. It is based on the fact that the plasma plume, which occurs under ablation of a target in air by high-intensity short laser pulses, can penetrate through a dense gas environment without significant cooling at the distance of about 1 mm. The technique has been applied to deposit diamond-like carbon (DLC) coatings on stainless steel substrates using four different values of pulse duration: 10 ns, 300 ps, 5 ps and 130 fs. Optimization of different experimental parameters including distance between the target and the substrate, laser intensity and gases (He, Ar, N₂, compressed air) blown in the deposition zone, has been performed. The deposition rate in the experiments was estimated as 2–5×10^-4 nm/(cm²pulse) for the pulse energy of 1–4 mJ. The deposited amorphous carbon films with thickness of several hundred nanometers have shown high average nanohardness (10–25 GPa depending on the irradiation conditions) and good adhesion to substrates (60 MPa). According to X-ray electron spectroscopy analysis the films consist of both sp²- and sp³-bonded carbon and contain 3–7% of free oxygen in bulk. The mechanisms of DLC non-vacuum laser deposition are discussed. To demonstrate the large potential of this technique, the first results on deposition of titanium nitride using ablation of titanium in air with nitrogen jet assistance are also presented. PACS 52.38.Mf; 81.15.Fg; 81.05.Uw     

探测大气中CO2的Raman激光雷达

基于大气激光后向散射光谱，研究和设计了探测大气CO₂浓度的Raman激光雷达,其发射机采用Nd∶YAG激光的三倍频354.7nm作为工作波长,发射的单脉冲能量350mJ,重复频率20Hz；接收机采用了光电倍增管(量子效率25%)和光子计数器(计数速率200MHz),探测CO₂的Raman散射371.66nm(频移1285cm^-1)信号,(1小时累加)近地面2.5km以内信噪比不小于8.采用组合滤光片来抑制强的354.7nm Mie-Rayleigh后向散射和氧气375.4nm Raman后向散射对信号的严重干扰. 比较分别来自大气CO₂和参考气体N₂的Raman后向散射回波,可反演出大气中CO₂的相对浓度. 关键词： 大气光学 激光雷达 Raman散射光谱 参考气体 Mie-Rayleigh散射     

A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N₂ and H₂O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.     

Off-resonant fifth-order response function for two-dimensional Raman spectroscopy of liquids CS2 and H2O

The off-resonant fifth-order response functions for two-dimensional (2D) Raman spectroscopy of molecular liquids CS2 and H2O are investigated by using molecular dynamics calculation. This spectroscopy, able to deal with a phase space dynamics, shows the existence of nodal lines in several polarization tensor elements [see L. Kaufman et al., Phys. Rev. Lett. 88, 207402 (2002) for experimental results]. The nodal property is found to arise from the dynamical couplings among rotational modes, not accounted for in a normal mode picture. The effects of anharmonicities and "mode coupling through polarizability" are also investigated by comparing the 2D Raman signal with a constant temperature velocity reassignment echo method.     

发散光长程空气传输受激转动拉曼散射效应

研究强激光长程空气传输受激转动拉曼散射(SRRS)效应,寻求抑制措施是高功率固体激光驱动器建造中需要解决的关键问题之一。采用数值模拟的方法研究了发散光长程空气传输SRRS效应的演化规律,通过几何近似理论推导了该效应有效建立时的强度距离乘积阈值和抑制判据。结果表明：发散光长程空气传输SRRS效应的建立速度小于平行光,二者阈值有理论关系;能够有效抑制SRRS效应的发散角设计判据由光束口径、激光强度及安全传输距离决定。     

发散光长程空气传输受激转动拉曼散射效应

研究强激光长程空气传输受激转动拉曼散射(SRRS)效应,寻求抑制措施是高功率固体激光驱动器建造中需要解决的关键问题之一。采用数值模拟的方法研究了发散光长程空气传输SRRS效应的演化规律,通过几何近似理论推导了该效应有效建立时的强度距离乘积阈值和抑制判据。结果表明:发散光长程空气传输SRRS效应的建立速度小于平行光,二者阈值有理论关系;能够有效抑制SRRS效应的发散角设计判据由光束口径、激光强度及安全传输距离决定。     

A new method for the detection of Raman scattering from atmospheric pollutants

The Fabry-Perot interferometer can be used as a periodic filter for the sorting of spectra using the rotational Raman effect. Thus it is possible to detect low concentrations of impurities in the presence of the major atmospheric constituents. The parameters of importance in making these measurements and the expected results from this technique are discussed from theoretical computations.     

Photothermal probe beam deflection measurement of thermal diffusivity of atmospheric air

We have used a modified photothermal probe beam deflection system with a back pumping configuration for the measurements of the temperature-dependent thermal diffusivity of atmospheric air. The results are consistent and reasonably well agree with the literature values. The measured thermal diffusivity values are the same for the same measuring temperature regardless of the beam offsets and the deflecting surface temperatures. For the gas with known temperature-dependent thermal diffusivity, this method can be used to deduce the temperature of a gas from the measured thermal diffusivity value.