Absolute measurements of radicals in visible-ultraviola regions

建立了一套腔衰荡光谱装置。尽管OH测量的光谱线宽很窄，但环境实验条件满足朗伯-比尔条件，因此测量结果呈线性。在常压条件下，该方法的检测限为1.5 × 10^9个分子/厘米^3，理论上可以提高到5 × 10^7个分子/厘米^3。这个值仍然比预期的灵敏度低，可能是由于腔的不稳定性，这将在未来得到解决。反射镜的反射率，腔的长度和噪声主要控制检测限。考虑将极限提高1000倍，实现了现有检测方法对OH的现场测量。

A cavity-ringdown spectroscopic apparatus has been built up. Though the spectral linewidth measured for OH was narrow, the ambient experimental conditions fulfill the Lambert-Beer conditions and therefore the linearity of the measurements. The detection limit was estimated as 1.5x10^9 molecules/cm^3 under the ambient pressure conditions.This detection limit can be improved theoretically to 5x10^7 molecules/cm^3. This value is still less sensitive than the expected limit, possibly due to the instability of the cavity, which will be solved in future.The reflectivity of mirrors, the length of the cavity, and noise mainly control the detection limit. The consideration was performed to improve the limit 1000 times, which realizes the field measurements of OH by the present detection method.