多普勒测风激光雷达中马赫-曾德尔干涉仪的视场展宽技术研究

Field-Widening Technology of Mach-Zehnder Interferometer in Doppler Wind Lidar

火星大气风速廓线探测对研究火星大气环境具有重要意义,基于马赫-曾德尔干涉仪的多普勒测风激光雷达相对于一般的相干/非相干多普勒测风激光雷达更适合于火星地基探测。为使马赫-曾德尔干涉仪对激光雷达中望远镜接收到的大视场角回波光信号进行频移检测,需要对马赫-曾德尔干涉仪进行视场展宽。对马赫-曾德尔干涉仪中棱镜式视场展宽技术与"猫眼"光学系统的视场展宽技术进行研究后发现,棱镜式视场展宽技术更具优势。设计并搭建了一套光程差为219 mm的马赫-曾德尔干涉仪,使用压电晶体扫描反射镜片的方式测量其对以11 mrad视场角入射的准平行光束的透射谱,得到干涉仪最大的干涉对比度为0.87,满足多普勒测风激光雷达的使用需求。结合地球大气环境分析了干涉仪干涉对比度随高度的变化,结果表明:虽然大光程差马赫-曾德尔干涉仪的干涉对比度在5 km以下低空大气中随高度增加有小幅下降,但仍可使用这种干涉仪进行大气风速探测。

Investigating the wind-speed profiles in the Martian atmosphere is significant for elucidating the Martian atmospheric environment. The Doppler wind-detection lidar based on the Mach-Zehnder interferometer is more suitable for Mars ground detection than the normal coherent/incoherent Doppler lidars. However, for detecting the frequency shift of the echo signal within the large field of view received by the Doppler lidar telescope, the Mach-Zehnder interferometer must be adapted by the field-widening technology. This study evaluates the effectiveness of two field-widening technologies-one based on a prism and the other based on the ‘cat’s-eye’ optical system-in a Mach-Zehnder interferometer. The prism-based technology proved more advantageous than the cat’s eye system. Next, a Mach-Zehnder interferometer with an optical path difference of 219 mm was designed and constructed. The designed Mach-Zehnder interferometer was injected with a quasi-parallel beam with an 11-mrad field of view, and its transmission spectrum was measured by scanning a mirror driven by a piezoelectric crystal. The maximum interference contrast of the interferometer was 0.87, sufficient for a Doppler lidar. The height dependence of the interference contrast was then analyzed in the earth’s atmospheric environment. Although the interference contrast of the Mach-Zehnder interferometer with a large optical-path difference decreased slightly with the increase of height in the low-altitude atmosphere(below 5 km), the atmospheric wind speed was still detectable with the interferometer.