移相自平衡激光吸收光谱技术的研究

Study on phase shift auto-balanced laser absorption spectroscopy

为了提高可调谐二极管激光吸收光谱(TDLAS)直接吸收技术的检测灵敏度,解决自平衡探测技术需要两条环境接近的光路而造成的适用性差的问题。采用了一种移相自平衡吸收光谱技术,该技术将信号经过滤波、放大和移相后,两个相差180°的信号经过反演就可提取出吸收信号,再对吸收信号及代表光强的直流分量信号进行数据处理便可测得气体浓度。分析显示移相自平衡吸收法能解决自平衡吸收法不能适用于同光路检测的原理性缺陷。结果表明,移相自平衡吸收光谱技术对信号的微小变化具有较高的灵敏度,信噪比也比直接吸收法提高了8倍～9倍,更适用于开放光路情况下的气体探测。为TDLAS在长距离气体检测领域提供了一个有效的高灵敏度探测手段,具有广泛的应用前景。

Tunable diode laser absorption spectroscopy （TDLAS） is a flexible and well-developed technology used for gas detection in open optical path. In order to improve the detection sensitivity in the direct absorbing method, and solve the adaptation of auto-balanced detection requiring two similar optical paths, a so-called phase shift auto-balanced detection was presented, in which after filtering, amplifying and phase shifting, the absorption signal could be obtained from two optical signals with phase shift difference of 180°; and then gas density could be calculated after processing the absorption signal and the direct current indicating the light intensity. The results show that phase shift auto-balanced detection can overcome the disadvantages of the auto-balanced detection for it can not be used in the same optical path. In addition, it is very sensitive to the subtle change of signal and the signal-to-noise ratio is improved greatly, 8 - 9 times higher than direct detection. The phase shift auto-balanced detection can provide a sensitive and stable approach to detect the long-range gas and may be used in wider areas in the future.