基于自级联光参量振荡技术的2.7微米波段激光特性及器件研究

2.7μm waveband laser have important application value in civilian, national defense and high-tech areas as laser medical treatment, laser bio-engineering, remote sensing and electro-optical countering. Recently, the laser source obtained by the different methods has its limitation. This project proposes a new self-cascaded optical parametric oscillation (OPO) laser using neodymium-doped laser crystal and single non-critical phase matching cut KTiOAsO4 crystal to obtain 2.7μm waveband laser. Cavity structure and film were reasonably designed to ensure that the signal light generated by the first OPO process was closed in OPO cavity. The signal light with high power intensity was adopted to pump the same KTA crystal to achieve efficient second OPO conversion. The compensation technique of mode mismatch for both fundamental and OPO cavities, as well as the high efficient pump technique with low thermal effect will be adopted to study the laser characteristics and key problems of self-cascaded OPO. A pulsed 2.7μm mid-infrared laser with low-threshold, high efficiency, compact structure and independent intellectual property rights will be developed, with the output power exceeded 3W. The research results are of great significance in clarifying the cascade OPO operation mechanism and developing efficient 2.7μm waveband laser output.

2.7微米波段激光在激光医疗、激光生物工程、气体遥感探测和光电对抗等民用和国防高技术领域具有重要的应用前景。目前不同方法获得的该波段激光光源均有其局限性。本项目提出了通过自级联光参量振荡（OPO）技术来实现2.7微米波段激光输出。以最成熟的掺钕离子激光晶体与单块非临界相位匹配切割的KTiOAsO4非线性光学晶体组合为研究对象，通过合理的谐振腔结构及膜系设计，将OPO产生的信号光封闭在腔内，以OPO腔内高功率密度的信号光泵浦同一块KTA晶体实现高效的二次OPO转换。利用复合腔模式失配补偿、低热高效泵浦设计等技术，研究自级联OPO激光特性及关键科学问题。研发获得低阈值、高效率、结构紧凑并具有自主知识产权的新型2.7微米波段中红外激光器，预期获得3W以上高重频脉冲激光输出。项目研究成果对阐明自级联OPO运转机制，实现高效的2.7微米波段激光输出具有重要意义。

2.7μm波段激光在大气污染、激光医疗、光电对抗等民用和国防等领域具有重要应用。本项目首次进行了基于非临界相位匹配砷酸钛氧钾（KTA）晶体的自级联光参量振荡（OPO）技术实现高效的2.7μm波段激光输出的研究。研究过程中分析了自级联OPO的热效应特点、复合腔模式匹配、高效变频转化机制等关键科学问题，分别利用Nd:YVO4、Nd:YLF、Nd:YAP和Nd:GdVO4等常用的激光晶体产生基频光驱动KTA晶体，并分析了级联OPO的输出激光特性。Nd:YVO4晶体热导性能差，在较低泵浦功率下就引起模式失配，导致转换效率低。在8.7W入射泵浦功率和60kHz重复频率下，获得了445mW的2.59μm激光输出；Nd:YLF具有较长的上能级荧光寿命，可在相对较低的重复频率下获得较高的输出平均功率。在9.7W入射泵浦功率和15 kHz重复频率下，获得了605mW的2.5μm激光输出，单脉冲能量可达40μJ；Nd:GdVO4晶体热导性较好，我们在更高的泵浦功率下获得了更高的平均输出功率。在13.4W入射泵浦功率和60kHz重复频率下，获得了1.1W的2.58μm激光输出，转换效率达8.2%。所以本项目成功验证了基于KTA级联自拉曼实现高效2.7μm波段激光输出的可行性。相关激光系统与普通的KTA-OPO实现1.5μm波段的激光系统一般大小，结构紧凑。本项目的研究在新型OPO方向有重要的学术价值，且2.7μm波段激光在民用和高技术领域存在重要的应用价值。