相敏式激光啁啾色散光谱技术在高吸收度情况下的应用  

Phase sensitive chirped laser dispersion spectroscopy under high absorbance conditions

作　　者：丁武文 孙利群[1] 

机构地区：[1]清华大学精密仪器系精密测试技术及仪器国家重点实验室,北京100084

出　　处：《物理学报》2017年第12期77-86,共10页Acta Physica Sinica

基　　金：国家重大科学仪器设备开发专项(批准号:2012YQ200182;2012YQ0901670602)资助的课题~~

摘　　要：研究了相敏式激光啁啾色散光谱法在高吸收度情况下的应用.用窄频半导体激光器作为光源,利用一工作于载波抑制模式的铌酸锂电光强度调制器调制单频激光,在单频激光两侧产生两个边频分量,并通过两边频分量产生外差干涉信号.利用外差干涉的相位波动来测量甲烷气体位于1653.7 nm附近的折射率波动,通过气体折射率与吸收系数之间的Kramers-Kronig关系计算甲烷气体浓度.传统的波长调制光谱法受限于郎伯-比尔定律,在应用于高吸收度的情况时,存在灵敏度下降的问题,甚至出现随气体浓度上升输出信号反而下降的现象.实验结果显示,相同实验条件下,波长调制光谱法的线性测量范围为38.1—1500 ppm·m,线性测量的动态范围仅为16 d B;而相敏式激光啁啾色散光谱法在很大的吸收度范围内均具有线性输出,检出限低至47.3 ppm·m,线性测量范围上限为174825 ppm·m,具有超过35 d B的动态范围.A whole-fiber methane sensor under high absorbance based on phase sensitive chirped laser dispersion spectroscopy is presented in this paper. The laser source of the sensor is a tunable distributed feedback diode laser with a frequency of 1653.7 nm. A telecom-based electro-optical intensity Mach-Zehnder modulator working in carrier suppression mode is adapted to modulate the single frequency laser beam for generating a dual-sideband spectrum beside the carrier wave. Unlike previous proposed phase sensitive chirped laser dispersion spectroscopy scheme, the beatnote signal generated by the two sidebands is detected experimentally. The refractive index fluctuation around the 2ν3 transition of methane is measured by detecting the phase variation of the dual-sideband beatnote signal through using the heterodyne inter-ferometric method. A lock-in amplifier is employed in the phase demodulation process. By connecting the refractive index （the real part of the complex refraction index） and the absorption coefficient （the imaginary part of the complex refraction index） via Kramers-Kroning relation, the gas concentration information is retrieved from the optical dispersion measurement. Absorption-based wavelength modulation spectroscopy measures the gas concentration encoded in the optical intensity based on Beer-Lambert＇s law. However, the signal sensitivity of wavelength modulation spectroscopy de-creases, and the signal even decreases while the gas concentration is raised in high absorbance condition, which leads to an uncertainty in concentration measurement. Experimental results demonstrate that wavelength modulation spectroscopy has better performance in low absorbance condition. The detection limit is about 38.1 ppm·m. However, because the sensitivity decreases in high absorbance conditions, the upper detection limit of wavelength modulation spectroscopy is only 1500 ppm·m. The dynamic range is defined through dividing the upper detection limit by the detection limit. Therefore, the wavelength modulatio

关 键 词：可调节半导体激光吸收光谱法 色散光谱 波长调制光谱 外差干涉 

分 类 号：O433[机械工程—光学工程]