痕量气体激光检测系统波长锁定技术研究

利用可调谐半导体激光吸收光谱技术(TDLAS)对痕量气体进行检测时,环境温度变化以及激光器控制电路的噪声常常使得激光器输出波长发生漂移,影响了气体浓度测量的准确性。以开放光路的激光吸收光谱氨气检测系统为例,在分析激光器扫描中心波长随电流变化规律的基础上,提出了基于电流控制的自适应锁定扫描中心波长的方法。研究了基于参考校准光谱的光谱数据对准算法,实现了开放大气中氨气浓度的实时监测。结果表明,波长锁定大大提高了痕量气体浓度反演的准确性和稳定性。氨气浓度具有日变化周期:上下班时段浓度上升,中午达到最大值,夜间浓度降低,系统检测限为3.8mg.m-3.m。     

Czerny-Turner正交型光栅单色仪的波长校准

研究了Czerny-Turner正交型光栅单色仪的波长校准技术。结合单色仪的结构参数和特点,提出以符合光栅方程的正弦曲线作为仪器出射波长的校准方程,基于最小二乘法原理给出校准方程的拟合残差表达式,由于校准方程的非线性,应用二维Nelder-Mead单纯形法求解拟合残差的待定系数,建立了波长与光栅转角的精确表达式,并通过实验验证了该算法的准确性。结果表明,经过校准的单色仪波长定位精度小于0.1nm,比设计要求提高一个数量级。该方法在Czerny-Turner正交型光栅单色仪的波长校准过程中,应用简单,容易实现,只需稍加修改步进电机的控制程序,即可完成对仪器出射波长的快速实时校准,实用性强。     

Photophysical properties and photostability of novel unsymmetric polycyclicphenazine-type D-π-A fluorescent dyes and the dye-doped films

Structural isomers of unsymmetric polycyclicphenazine-type D-π-A fluorescent dyes have been newly synthesized and characterized in both solution and polymer films. The dyes exhibited two strong absorption bands at around 328-401 nm and 516-532 nm, and an intense fluorescence band at around 595-629 nm (Φ = 0.32-0.84) in 1,4-dioxane. The dye-doped polymer films showed good ability of wavelength conversion; the films can efficiently convert ultraviolet and green-yellow lights into red light (Φ = 0.43-0.86). Moreover, the photostability of the dyes-doped PS, PMMA, and PLA films has been investigated.     

Selection of Wavelength Range and Number of Factors to be Used in the PLS Treatment of Spectrophotometric Data

Abstract

A procedure for selection of wavelength range and number of factors to be used in partial least square calibration that involves the calculation of prediction residual sum of squares (PRESS) in different conditions is proposed. The best model takes into account the minimum PRESS value that does not show significant differences with respect to the corresponding model with fewer factors. The ability of the proposed method to minimize errors in partial least squares (PLS) prediction is demonstrated by applying it to the resolution of phenytoine (DPH) and phenobarbital (PB) binary mixtures with errors less than 2.8%; the results are compared with those obtained using another wavelength selection procedure. The ensuing method, which was validated by high performance liquid chromatography (HPLC), also gives good results with real samples (pharmaceutical preparations).     

窄带吸收光谱扫描技术在气体定量检测中的应用

提出一种基于窄带气体吸收光谱扫描技术的气体定量测量系统。利用可调谐光纤滤波器(TOF)输出的窄带光作为探测光,结合波长调制技术,克服不同气体间的交叉敏感,提高了对环境中待测气体测量的选择性。为克服TOF非线性特性对测量结果的影响,提高系统运行稳定性,系统以光纤光栅反射光谱作为参考波长,实现了TOF透射光波长调制范围以及调制中心的稳定控制。为提高系统测试灵敏度,开发了以同步累积器为核心的微弱信号检测电路,实现了系统微弱响应信号的高灵敏度提取。以乙炔气体为实验气体,通过实验证明系统响应与输入乙炔气体浓度之间具有良好的线性关系。当信噪比为3时,系统最低检测限为5×10-6。     

Scattering by inhomogeneous particles: microwave analog experiments and comparison to effective medium theories

It is common practice to use effective medium theories (EMT) to estimate average, “effective” optical constants of inhomogeneous materials. A variety of EMTs were developed for different internal structures of the medium and for a variety of shapes, size distributions and physical properties of the inhomogeneities. The most popular EMTs (Maxwell Garnett, Bruggeman, Looyenga, etc.) consider inhomogeneities that are much smaller than the wavelength. The so-called extended EMTs were developed to find effective optical constants in the case of inhomogeneities comparable and slightly larger than the wavelength. This paper compares angular distribution and wavelength dependence of intensity and polarization of scattered light obtained from calculations using the most popular EMTs and extended EMTs with the results of microwave analog measurements at the microwave facilities of the University of Florida. We simulated the light scattering by organic grains with silicate inclusions of size parameter x=0.075 (≈0.01 μm), 0.60 (≈0.1 μm), and 1.24 (≈0.2 μm). The conclusion is that for inclusions of a small size and for a small volume fraction of them in the mixture all EMTs yield similar results and show reasonable agreement with experimental results. The accuracy is better for the angular dependencies of the intensity and of the polarization of the scattered light than for their wavelength dependencies. For inhomogeneities comparable and larger than the wavelength extended EMTs work better but for smaller inclusions non-extended EMTs show more accurate results. Large volume fractions of the inclusions in the mixture (>10%) essentially reduce the accuracy of the results obtained with EMTs. Based on our study we do not recommend to use EMTs in the back-scattering domain and at the scattering angles 30°<θ<70°.     

在周期性极化铌酸锂波导中的波长转换与光谱分析

实验研究了在准相位匹配LiNbO₃波导中级联的倍频和差频波长转换,通过对转换频谱分析和波形对比分析,讨论了在脉冲泵浦情况下走离效应对光脉冲之间波长转换的影响：由于波导的色散性能,不同波长的光脉冲在波导中传播具有不同的群速度,处在0.8 μm光波段的倍频光脉冲比处在1.55 μm光波段的泵浦光脉冲的传播速度慢,导致了倍频光脉冲与泵浦光脉冲在传播的过程中发生走离;因此倍频脉冲在频域被压缩而在时域被展宽,并遗传给差频过程使得转换脉冲的谱宽变窄、脉宽增加、占空比变大,表明脉冲光泵浦波长转换对信号频谱及波形不是严格透明的转换。实验同时实现了一对多通道的波长转换,表明连续控制光的线宽对转换信号的信噪比有较大的影响。     

红外光谱统计波长选择方法用于废气检测

为了从含有噪声的大气红外光谱中提取微量待测污染组分的定量特征,进而建立校正模型,本文提出了一种基于统计理论的波长选择方法。该方法针对待测组分,在对光谱各波长位置的噪声强度进行统计估计的基础上,提出了选择最佳波长子集的目标函数。该目标函数包含波长子集的噪声和长度参数,这使得在最小化模型误差的同时也防止了模型规模的无限制膨胀。为了检验该方法的性能。文章利用含背景噪声的实测光谱数据针对三种气体进行了波长选择,并利用神经网络技术分别建立了校正模型。实验结果与波长子集的优化结果相符,所选择的波长子集的长度不足光谱波长总点数的2％,同时,光谱中的噪声也在校正模型中得到了明显的抑制。实验结果证明了该波长选择方法的有效性。     

Wideband multiwavelength erbium-doped fiber ring laser with frequency shifted feedback

Wideband multiwavelength erbium-doped fiber ring lasers with frequency shifted feedback are described. The use of an intra-cavity gain flattening filter (GFF) was proposed in order to increase the lasing spectral bandwidth, leading to a demonstration of 34 lasing wavelengths in 28 nm bandwidth in C-band. The GFF induced spectral output power fluctuation is discussed. Multiwavelength operation was also demonstrated for the first time in L-band, where wideband laser operation was obtained without a GFF. Optical bistability and Kerr effect induced pulsation were determined to be limiting factors to stable operation range in this kind of multiwavelength lasers.     

天然气管道泄漏可调谐二极管激光遥感探测的研究

天然气管道泄漏不仅造成经济损失而且是危险之源。传统的天然气管道泄漏检测技术效率低、速度慢,难以满足实际应用的需要。近年来以近红外二极管激光吸收光谱为基础的光学传感器由于具有灵敏度高、体积小、重量轻和无需维护等优点而得到了广泛的应用。文章以可调谐二极管激光吸收光谱和谐波探测技术为基础进行天然气管道泄漏遥感探测技术的研究,采用二次谐波与一次谐波信号的比值作为系统浓度标定,结果显示浓度与比值之间具有较好的一致性。文章还就不同地形散射体对探测结果的影响进行了测量和分析,实验结果表明二次谐波与一次谐波信号比值标定技术对便携式二极管激光光学测量能够很好的满足实际应用的需要。