基于多纵模激光器的高光谱分辨率激光雷达研究

High-spectral-resolution lidar (HSRL) can retrieve optical properties of atmospheric aerosols accurately and independently by separating the Mie and Rayleigh components in the lidar return spectrum, and receiving more and more interests. Current HSRLs adopt single-longitudinal mode lasers to ensure the narrowband spectral distribution in the lidar return, and then iodine absorption cells or interferometers are employed as the spectral discrimination filters to obtain fine Mie-Rayleigh spectral separation. However, available single-longitudinal mode lasers for HSRL require accurate controls for the laser resonant cavity length and pulse establishment time, inducing susceptible environmental adaptation and limiting the stability of current HSRLs in harsh environment outside laboratories (such as airborne and satellite-borne applications). This project aims to investigate a new HSRL concept, called HSRL technique with a multimode laser, which can work using a multimode laser as the transmitter. It takes advantage of the period characteristic of the spectral function of the interferometric spectral discrimination filter (ISDF) thoroughly. By matching the spectral period of the ISDF with the mode interval of the multimode laser, and locking the transmission peak (or valley) to the central frequency of each mode, fine spectral discrimination for the lidar return from each longitudinal mode can be obtained. This HSRL can directly benefit from the relatively mature multimode laser technique without any dependence on the complicate and flimsy single-longitudinal mode laser, thus reduce the size, capital cost, and promote the stability and environmental adaptation of the HSRL transmitter more easily. We believe the study of this technique would contribute a lot to the future HSRL developments.

高光谱分辨率激光雷达(HSRL)通过分离回波信号中的米散射和瑞利散射成分，可直接较高精度地反演大气气溶胶光学参数，受到越来越多的关注。当前的HSRL均采用单纵模激光器以保证大气回波具有较窄的频谱分布，继而用碘分子吸收池或干涉仪作为光谱鉴频器实现米-瑞利散射信号的精细光谱分离。而能用于HSRL的单纵模激光系统需对谐振腔腔长及脉冲建立时间等参数进行精确控制，环境适应性较差，限制了当前HSRL在实验室以外复杂环境下(如机载、星载等)的稳定运行和广泛应用。拟研究一种能采用多纵模激光器作为发射光源的多纵模HSRL技术。充分利用干涉光谱鉴频器的周期鉴频曲线，通过将其设计得与激光器纵模间隔相匹配，并将其透射峰(或谷)锁定至每个纵模频率中心处，实现多纵模回波信号的精细鉴频。该HSRL不再依赖于复杂脆弱的单纵模激光器，利用成熟的多纵模激光技术即可提升系统稳定性和适应性、降低成本并减小体积，具有较好应用前景。

高光谱分辨率激光雷达（HSRL）通过分离大气回波信号中的米散射和瑞利散射成分，可直接较高精度地反演大气气溶胶光学特性参数，受到了越来越多的关注。当前的HSRL大多采用单纵模激光器作为发射光源，结合吸收型或干涉型光谱鉴频器实现米-瑞利散射信号的精细光谱分离。用于HSRL的单纵模激光器大多采用种子注入方式实现，导致激光系统研制成本较高，体积庞大。种子注入激光系统需要对谐振腔设计参数及脉冲建立时间等精确控制，环境适应性较差，限制了当前HSRL在复杂环境下（如机载、星载等）的稳定运行和技术推广。相比于单纵模激光技术，多纵模激光技术更加成熟且容易实现；当HSRL系统采用干涉光谱鉴频器时，由于光谱鉴频曲线的周期性，使单纵模激光不再成为研制HSRL系统的必备条件。. 本项目研究了一种以多纵模激光器作为发射光源，结合干涉光谱鉴频器鉴频的多纵模HSRL技术，实现了大气气溶胶光学特性参数的探测与反演。通过充分利用干涉光谱鉴频器的周期性光谱鉴频曲线特性，使得激光器与鉴频器光谱匹配，实现HSRL高精度光谱鉴频。项目完成了多纵模激光器的研制，最终建立了一套多纵模HSRL原理性实验系统。 . 通过项目组四年的研究，建立了多纵模HSRL理论体系与反演算法，为多纵模HSRL系统反演大气气溶胶光学特性参数提供指导；根据该理论体系研制了用于多纵模HSRL光谱鉴频的干涉光谱鉴频器——视场展宽迈克尔逊干涉仪FWMI；提出了用于HSRL系统的多纵模激光器技术指标，完成了多纵模激光器工程样机的研制，实现了多纵模激光器与FWMI的光谱匹配。本项目最终建立了一套多纵模HSRL原理性实验系统，探测反演获得了1-2km的大气气溶胶光学特性参数。多纵模HSRL反演的气溶胶激光雷达比为40-60sr，将反演结果同历史数据以及现有稳定运行的激光雷达进行比对表明，多纵模HSRL系统能够较为可靠地实现大气气溶胶光学特性参数的反演。本项目圆满完成了预期的各项研究内容，研究成果可降低HSRL系统研制成本，减小系统体积，并提升HSRL稳定性与环境适应性，在大气光学遥感领域具有较好的应用前景。