注入激光引发级联效应对提高氟化氢激光单谱线输出效率的作用机理研究

The hydrogen fluoride (HF) chemical laser is one of the most successful high-energy laser on account of the advantages including high energy conversion efficiency, low diffraction loss in long-range transmission, excellent amplification characteristics, etc.. However, several spectral lines with high rotational energy level in the range of long wavelength area of HF chemical laser have fine atmospheric transmission. As a new technology developed to concentrate laser energy on these spectral lines, there will be profound effects on high energy HF laser application. This project intends to provide a novel scheme to improve output efficiency of HF spectral lines weakly absorbed by atmosphere. The distributions of populations on the energy levels of transition line will be altered by a cascade effect caused by laser injection. The output power of the target line will be improved due to this process. 1)A HF laser physical model based on cascade effect will be established to study the mechanism of transition of populations theoretically. 2)High sensitivity detection technique will be used to study the interrelationship of the cascade effect, vibration rotation relaxtion, injected laser, and output spectral line. 3)The characteristic parameters of laser dynamic model will be consummated, also the laser operational parameters will be optimized, in order to demonstrate single target line oscillation and laser output enhancement. This project is meaningful for further studying the complicated operation process and wavelength control of HF chemical laser.

氟化氢（HF）化学激光以其能量转化效率高、远距离传输衍射损耗小、工程放大性好等特点，是目前最成功的高能激光之一。HF化学激光中只有极少数长波区域高转动能级的跃迁谱线具有较好的大气传输性能。如果能够将激光能量集中于这些谱线，将会对HF高能激光的应用产生深远影响。本项目提出一种提高HF激光大气弱吸收单谱线输出的新机制，通过外部注入激光引发HF激光的级联效应，改变跃迁谱线能级上的粒子数分布，从而实现目标谱线的增强。主要内容有：1）建立基于级联效应的选线HF激光动力学模型，从理论上探究影响能级粒子跃迁的机理和规律；2）利用高灵敏度测量技术，研究级联效应、振转弛豫、外部光场等对振动—转动能级粒子数分布及谱线跃迁的作用机制；3）完善动力学模型特征参数，优化激光器参数，最终实现HF激光特定单谱线输出增强的出光演示。本项目对于深入研究HF化学激光复杂的运转过程及激光波长调控的进一步发展具有重要的实际意义。

中红外氟化氢（HF）化学激光是目前发展最成熟、最具规模的化学激光器。传统的HF化学激光为多谱线输出体系，大气中的水汽会对这些谱线产生强烈吸收，这极大地限制了HF激光的应用。研究表明，HF化学激光中有极少数高转动能级的跃迁谱线恰好位于大气透过精细窗口，将激光能量集中于大气弱吸收谱线，是HF化学激光突破实际应用瓶颈的关键。. 根据气体动力学、化学反应动力学及受激辐射跃迁的相互作用，建立了HF化学激光产生的数学模型，并实现了HF激光输出的数值模拟计算。计算结果表明化学反应速率能够显著影响振动能级粒子数分布；在高振动能级上，转动能级分布服从平衡Boltzmann 分布，而在低振动能级上，转动能级分布偏离平衡Boltzmann分布。基于模拟计算模型，对HF激光器的增益特性进行模拟计算，为实验的设计优化提供参考。. 采用自发辐射荧光光谱法，对HF受激辐射粒子的振转能级分布进行了实验研究。采用吸收光谱法，对HF基态粒子的分布进行了实验研究。实验上获得了HF振转能级上的粒子数分布。采用吸收光谱法得到了基态粒子对HF激光谱线的吸收特性，实验结果表明，基态粒子对低振动能级谱线具有强烈吸收，而对高振动能级谱线吸收相对较小。. 分别采用光腔腔镜镀截止膜和衍射光栅作为腔镜的方法实现了大气弱吸收谱线的选线输出，并在不同光腔参数条件下对谱线的输出特性进行了研究，采用最佳光腔参数时，大气弱吸收谱线由传统HF激光器出光占比极小提高至占全谱输出能量的25%。. 在选线HF激光器的基础上研究了级联效应对HF激光谱线线输出的影响。实验结果表明，针对大气弱吸收谱线，当其所对应的上能级谱线跃迁出光时，目标谱线的输出提高了30%；当其所对应的下能级谱线跃迁出光时，目标谱线的输出大幅降低，甚至无法出光。由此，导通其上能级谱线出光，是实现大气弱吸收谱线输出增强的有效途径。