基于LD泵浦碱金属蒸气激光器的窄谱宽双波长中红外光参量振荡技术研究

A continuous-wave (CW) tandem optical parametric oscillator (OPO) is researched in this project. It has the features of compact configuration, narrow spectral width, and dual-wavelength co-axial propagation. In this project, diode pumped alkali vapor laser (DPAL) is adopted as the pumped source to obtain CW tandem OPO with dual mid-infrared wavelength. Compared with the common OPO pump source, the wavelength of DPAL is shorter and the energy of single photo is higher. Accordingly, the power duty and intensity of the first signal beam will be higher, which results in low threshold of the second OPO. Meanwhile, a dual-period MgO doped periodically poled lithium niobate (MgO:PPLN) with poled periods of periodical cycle is used to improve the coupling of the parametric beams. By this method, the heat accumulation will be reduced and regular laser power intensity will be formed, which will be useful to obtain a uniform pole period by compensating the heat-induced period variation. Based on the technical routine, the spectral width of the tandem OPO will be narrower than 1.5 nm, and the laser with the wavelength of 3314 nm and 3304 nm will emit co-axially. The OPO can be used as the laser source for differential absorption Lidar, and will offer a feasible technical route for other differential absorption Lidar sources.

本项目提出一种连续波级联中红外光参量振荡器（OPO），具有结构简单、窄谱宽、双波长共光轴传输的特点。项目中，利用LD泵浦碱金属蒸气激光器较目前常用的OPO泵浦源输出激光波长短、单光子能量高的特点，提高一级OPO信号光的功率占比和功率密度，降低级联OPO的阈值功率，并使两次OPO输出的闲频光波长不同，实现连续波的双波长激光输出。同时采用周期交替的双周期掺镁周期极化铌酸锂晶体作为准相位匹配晶体，提高非线性晶体内各参量光之间功率密度的耦合度，减少热累积，并形成较为规律性的光强分布，通过热补偿晶体极化周期的方式提高OPO工作时晶体极化周期的均匀性。基于该技术路线搭建的OPO将能够输出谱宽小于1.5nm的3314nm和3304nm的激光，满足激光差分吸收探测甲烷雷达的应用，为其他气体的激光差分探测雷达激光源的研制提供切实可行的技术路线。

本项目旨在解决窄谱宽双波长共光轴连续波中红外激光的产生问题。在无线宽控制元件的谐振腔结构下，实现窄谱宽的双波长中红外激光光束，为差分吸收探测甲烷气体浓度提供优质光源。通过中心开孔的离轴抛物面镜实现线偏振的泵浦光和铷激光的共光轴耦合，同时，将窗口高平行度的碱金属气室以布儒斯特角放置，抑制了寄生振荡的产生；通过优化电极设计降低高压脉冲电场导致的尖峰效应，优化设计施加的电压波形、电压幅值等参量，精确控制等极化反转过程中的极化区的横向扩张，制备出一级周期和二级周期占空比均接近50%的高品质周期交替MgO:PPLN晶体；将这种双周期的不同周期占比的MgO:PPLN的用于铷蒸气激光泵浦掺钕晶体的光参量过程，获得了双波长中红外激光输出。.在本项目资助下，在Scientific Report、Optics Communications、中国光学、SPIE等学术期刊或学术会议上发表学术论文13篇，受理或申请国家发明专利8项。较为系统地研究了铷蒸气激光级联泵浦中红外激光在实用化工程化进程中面临的问题，建立了较为完善的级联泵浦时的谐振腔设计模型，阐述了碱金属激光器的寄生振荡现象及其机理，并提出了抑制寄生振荡的方法，实现了中红外窄谱宽的双波长激光输出，将推动中小功率中红外激光器在气体探测领域的应用。