A Tunable IR Laser Source for Remote Sensing

基于CO 2激光器在微波频率下的高效相位调制，构建并表征了一种发射范围在9-12 μ m范围内的宽可调谐紧凑红外激光源。该激光源由稳定在4.3 um发射Lamb-dip的选线co2激光器和行波CdTe缓冲BaAs微带电光调制器组成。它具有20 W的微波驱动功率，可以在与激光载波频率偏移8至18 GHz的频率上提供10至50 mW的连续可调谐红外功率输出。该源的性能和实用性将通过进行直接饱和吸收和herodyne测量来评估和证明。饱和吸收测量可以提供亚多普勒分辨率的原子和分子跃迁的单个谱线。这种可调谐激光器也将用作外差光谱仪的本振，可以显著提高系统的灵敏度。研究发生在低密度、低温区域的行星大气中的有趣现象需要一台超高分辨率、极低噪声的红外外差光谱仪，在这些区域需要亚多普勒光谱分辨率来完全解析线形并在空间上映射源。从红外外差测量中获得的信息可以准确地确定行星大气的压力、温度、激发和分子丰度。同样的技术也将应用于地球大气中微量气体的遥感测量。//

A widely tunable and compact IR laser source emitting in the 9-12 um range based on very efficient phase modulation of CO 2 lasers at microwave frequencies will be constructed and characterized. This laser source consists of a line selecting CO 2 laser, which is stabilized to the 4.3 um emission Lamb-dip, and a traveling-wave CdTe buffered BaAs microstrip electrooptic modulator. With a 20 W microwave drive power, it can provide a continuously tunable IR power output of 10 to 50 mW at frequencies 8 to 18 GHz off-set from the laser carrier frequency. The performance and usefulness of this source will be evaluated and demonstrated by carrying out both direct saturation absorption and hererodyne measurements. The saturation absorption measurements can provide individual line profiles of atomic and molecular transitioons with sub-Doppler resolution. This tunable laser will also be used as a local oscillator in a heterodyne spectrometer which can provide a significant improvement in system sensitivity. An ultra-high resolution and extremely low noise IR heterodyne spectrometer is required for the study of interesting phenomena in the atmospheres of planets occurring in low density, low temperature regions, where sub- Doppler spectral resolution are needed to resolve fully the line shapes and to map spatially the source. The information retrievable from IR heterodyne measurements can accurately determine pressure, temperature, excitation, and molecular abundances of planetary atmospheres. The same technology will find applications in remote sensing measurements of trace gases in the earth's atmosphere.//