光声光谱仪用三维扩展光源光场整形系统设计与实验

Design and experiment of light field shaping system for three-dimensional extended light source used in photoacoustic spectrometer

三维非相干扩展光源相比红外激光光源具有功率高、光谱范围宽、价格低等优势,在高精度、多组分光声光谱仪中具有极高的应用价值.然而,其存在方向性差、能量密度低、形状不规则等现实问题,需要在光学系统设计过程中进行光场整形.光声光谱仪要求在小体积范围内收集并优化厘米级三维扩展光源向全空间的辐射,经一系列波长及频率调制元件后,最终实现毫米级半径、厘米级长度的圆柱体光场分布.本文根据光学扩展量概念和边缘光线原理,在光学系统设计与优化的过程中突破传统完全基于点光源的设计模式,贯穿了扩展光源概念,基于自行设计的测量方法和装置直接获取了三维扩展光源的发光特性,并以微元的形式进行精准三维扩展光源建模.借助非球面实现了光声光谱仪用三维扩展光源光场整形系统的设计并进行了相关实验验证.以Hawkeye IR-Si272光源为例,分别实现了光声光谱仪光声池入池光功率和侧壁噪声仿真值与实验值的较小偏差,二者具有一致性.相比原厂聚光系统,自行设计的光声光谱仪用光源系统入池光功率从0.86 W提升至1.32 W,侧壁噪声从50.3%下降至19.7%,实现了百万分之一量级微量气体浓度检测.

Compared with infrared laser sources,the three-dimensional incoherent extended light source has the advantages of high power,wide spectral range,and low cost.It has extremely wide applications in highprecision and multi-component photoacoustic spectrometers.However,it encounters some problems about poor directivity,low energy density,irregular shape,light field shaping needed in the design of optical system.The photoacoustic spectrometer is required to collect and optimize the radiation of the centimeter-level threedimensional extended light source to the whole space in a small volume.Through using a series of wavelength and frequency modulation elements,the final cylindrical light field distribution with millimeter-level radius and centimeter-level length is realized.According to the concept of optical expansion and the principle of edge light,this paper breaks through the traditional design mode based on point light source in the process of optical system design and optimization.The concept of extended light source is used throughout the design process.The luminous characteristics of the three-dimensional extended light source are directly acquired by the selfdesigned measurement method and device which is accurately reflected in the three-dimensional extended light source model in the form of micro-element.The design of the light field shaping system of the three-dimensional extended light source for the photoacoustic spectrometer is realized by the aspheric surface,and the relevant experimental verification is carried out.Taking the Hawkeye IR-Si272 light source for example,the experimental value of the light power at the entrance of the photoacoustic cell and the sidewall noise rate of the photoacoustic spectrometer have a small deviation from their corresponding simulation values.Compared with the original condenser system,the self-designed photoacoustic spectrometer light source system increases the value of the light power at the entrance of the photoacoustic cell from 0.86 W to 1.32 W,and reduces the value of the sidewall noise rate from 50.3%to 19.7%.The lower limit of detection of the concentration of trace gas in the order of ppm(parts per million)is also achieved.