DEVELOPMENT OF DETECTION METHOD FOR MEASURING AMBIENT NO CONCENTRATION USING HIGH SENSITIVE LASER SPECTROSCOPIC TECHNIQUE

设计并搭建了真空室和真空系统，用于测量环境NO浓度。构建了脉冲nd: YAG激光器三次谐波抽运可调谐染料激光器的激光系统。染料激光器输出功率加倍，激发NO分子达到单反振动能级。对旋转温度进行了分析，确定在X/D = 70的条件下，旋转温度为25 K。在激光功率依赖实验中，我们再次确认了共振增强双光子电离（RETPI）过程，该过程的激光功率依赖指数为1.75。采用离子计数系统检测离子信号，提高信噪比。我们发现，将检测系统从模数运算改为离子计数运算后，灵敏度提高了近两个数量级。当NO浓度达到200 ppb时，离子信号呈线性响应。在化学方面。在NO_2干扰下，NO_2的灵敏度比NO高约2%。这表明冷却过程提高了选择性。检测限估计为16 pptv，积分时间为1 min。

we designed and constructed vacuum chamber and vacuum system for measuring ambient NO concentration. The laser system of tunable dye laser pumped by 3rd harmonic of pulsed nd : YAG laser was constructed. The out-put of dye laser was doubled to excite NO molecule into single ro-vibronic level. The analysis of rotationnal temperature was done to determine rotational temperature to be 25 K under X/D of 70. we reconfirmed resonance enhanced two photon ionization (RETPI) process rom the laser power dependence experiment showing index of 1.75. we employed ion counting system for detection of ion signals to increase S/N ratio. we found almost of two order of magnitude improvement of sensitivity by replacement of detection system from analog-to-digital operation to ion counting operation. we confirmed linear response of ion signal with NO concentration up to 200 ppb. In the chemical. interference of NO_2, the sensitivity of NO_2 is ca.2% compared to that of NO.This shows the improvement of selectivity by the cooling process. The limit of detection was estimated to be 16 pptv with an integration time of 1 min.