Atmospheric Trace-Gas Detection Using Very High-Sensitive Laser Sensors

大气痕量气体的高灵敏探测在臭氧层破坏、酸雨等地球大气环境问题中具有重要意义。本研究的目的是建立在1 ~ 10大气压条件下检测ppt量级微量气体的方法<-3>。在实验室原型模型的实验中充分利用了紧凑型激光源的最新发展。1.对于空间传输实验，我们构建了一个配备适当窗口的真空系统。选择乙炔作为在1.5 μ m波长范围内有吸收的样品。分布反馈（DFB）型的二极管激光器主要用作源。采用高灵敏度的吸收光谱法，利用电流调制测量了激光源的吸收跃迁矩和扫描特性等基本参数。一种更灵敏的方法是， ...更多信息 ch基于由高反射镜构成的法布里-珀罗谐振腔。使用长度为0.25 m的吸收池，我们观察到对应于2 m的等效吸收长度的信号，验证了增强效应。进一步提高谐振腔结构的稳定性和光源的稳定性将有助于谐振腔型传感器的发展。2.作为多模方案的一个例子，利用全光纤环形激光谐振腔进行了痕量气体检测实验。利用掺铒光纤放大器作为光源，通过带通滤波器实现了0.04nm的窄带宽。本文设计了一种可直接与光纤连接的专用气室，用于观察乙炔在1.5 μ m处的吸收。在适当的条件下，当抽运功率接近阈值时，激光输出功率随乙炔气压的变化较大。该传感器在检测由泵浦功率确定的压力范围内的痕量气体的非常微小的压力变化方面也表现出优异的性能。系统损耗的进一步降低确保了非常紧凑的全光纤痕量气体传感器的发展。少

High-sensitive detection of atmospheric trace-gases is becoming more and more important in the environmental issues concerning the earth's atmosphere such as destruction of ozone layrs and acid rain. The purpose of this research is to establish the method of detecting trace gases of ppt order under 1 atm to 10^<-3> atm conditions. The recent development of compact laser sources is fully exploited in the experiments with prototype laboratory models.1.For the spatial propagation experiment we have constructed a vacuum system equipped with appropriate windows. Acetylene is chosen for The specimen that exhibits absorption at the wavelength region of 1.5 mu m. A diode laser of distributed-feedback (DFB) type is mainly used as the source. Fundamental parameters such as the transition moment of the absorption and scanning characteristics of the laser source are measured with the method of highly sensitive absorption spectroscopy using current modulation. A more sensitive method is the one whi … More ch is based on a Fabry-Perot resonator constructed with highly reflective mirrors. Using an absorption cell of 0.25 m in length, we have observed a signal corresponding to an equivalent absorption length of 2 m, verifying the enhancement effect. Further increase of the stability of the resonator structure and that of the light source will lead to development of the sensors of resonator type.2.As an example of the multi-mode scheme, a trace-gas detection experiment has been performed using an all-fiber, ring-laser resonator. An amplifier based on Er-doped fiber is utilized as a light source, and a bandwidth as narrow as 0.04 nm has been attained with band-pass filters. A special type gas cell that can be directly connected with optical fibers is devised to observe the acetylene absorption at 1.5 mu m. Varying ring configurations, we have found that under suitable conditions the change of laser output power with acetylene pressure becomes large when the pumping power is close to the threshold. This sensor exhibits excellent performance also in detecting very slight pressure change of the trace gas in a pressure range determined by the pumping power. Further decrease of the system loss ensures the development of a very compact, all-fiber trace-gas sensor. Less