基于金刚石级联拉曼的连续波可调谐深紫外激光器关键问题研究

Raman spectroscopy, which adopted continous-wave tunable deep ultraviolet(DUV) laser (<260 nm) as excited source, has many advantages in anti-interference ability and sensitivity .It has been widely used in a broad fields such as: Chemistry, Biology,Materials and so on. However, current used DUV lasers are low efficient, big volumes and expensive. Therefore, finding a new alternative way to realize DUV lasers is important and significant for scientific and practical application. In this study, we propose a new strategy to obtain DUV lasers,which are base on blue laser pumped diamond Raman lasers and intra-cavity sum frequency mixing (SFM) and second harmonic generating (SHG) technologies. Theoretically, constructing a physical model of intra-cavity SFM and SHG cascade Raman laser, clarifying the physical mechanism of continuous wave cascading Raman lasers' generation and high efficient and stable operation. Experimentally, using 808nm LD dual pumped Nd:GdVO4/LBO 456nm laser and birefringent filter(BF) as a frequency selector to obtain high power single frequency blue laser operation, through enhanced effect of blue laser oscilating in the Raman cavity to reduce the SRS and CSRS threshod of diamond, using BBO crystal as frequency doubler and inserted it into the cavity to genearte DUV light. Throug SHG and SFM between the pump light ,first and second Stokes light, continuous wave DUV lasers between 228 nm and 260 nm can be generated, the maximum output power is more than 10 mW. This study will give a novel way to obtain the DUV laser with wavelength less than 260 nm. It will accelerate the applications of DUV in spectroscopy study, on the other hand, this DUV laser also can be used in many other basical and important areas. At last, the succesful completion of this project will further consolidate and strengthen our country's competitiveness and compactness in DUV laser and DUVLRS field.

波长小于260nm连续波可调谐激光源在深紫外拉曼光谱仪中具有重要的应用前景，现有深紫外光源因效率低、体积大、价格高等不足限制了深紫外拉曼光谱仪的应用与普及，因此，探索波长小于260nm的连续波可调谐激光源具有重要的科学价值和现实意义。本项目基于456nm蓝光外腔谐振泵浦金刚石拉曼激光器，通过腔内和频获取波长小于260nm连续波可调谐深紫外光源。理论上，通过构建腔内和频级联拉曼激光器理论模型，阐明连续波级联拉曼和频激光器形成和高效稳定运转的物理机理，为实验研究该类激光器提供理论指导。实验上，利用双端泵浦和组合双折射滤光片选频技术获得大功率单频蓝光输出；利用蓝光在拉曼腔中的谐振增强效应，降低金刚石级联拉曼阈值；通过BBO晶体腔内和频实现228-260nm连续波可调谐输出。本项目的成功实施将为连续波可调谐深紫外激光器产生提供一条新途径，将有助于加强和巩固我国在深紫外激光领域的影响力和竞争力。

激光拉曼光谱是研究物质分子振动和分子结构的重要工具，在催化科学、生物科学、纳米材料和食品安全等领域具有重要的应用前景。其中波长小于260nm的连续波可调谐激光器为激发源的深紫外拉曼光谱仪具有更好的抗干扰能力和灵敏度，是目前当前的研究热点之一。本项目通过腔内泵浦金刚石获得级联拉曼多波长输出，通过腔内和频技术实现波长小于260nm的深紫外激光输出。项目主要从金刚石的泵浦源——单频蓝光激光器，可见光泵浦连续波级联拉曼激光产生，腔内和频产生多波长深紫外激光源这三个方面开展理论和实验研究。在理论和技术路线上都进行了有益探索，获得了一些较重要的实验成果，积累了一些宝贵的技术方案和经验工艺。. 理论方面，在连续波自拉曼激光速率方程的基础上，对外腔谐振泵浦拉曼激光器及其腔内含有非线性和频转换的激光器的动力学过程进行了理论建模，通过数值仿真定性分析了和频输出功率随泵浦功率水平、拉曼增益、非线性转换系数等参数的变化关系，并获得了一些重要的结论，对该类激光器的动力学过程深入研究和分析具有重要理论借鉴和指导意义。. 在单频蓝光的产生方面，我们进行了组合双折射滤光片理论设计和激光实验研究，利用二类相位匹配晶体初步实现了低阈值单频457nm 蓝光输出，并制作出蓝光实验样机。根据外腔谐振功率水平和单频稳定性的要求，优化了单频蓝光方案，新方案的理论仿真分析已结束，实验验证工作还在进行中。. 在腔内谐振泵浦金刚石拉曼激光器实验研究方面，从CVD单晶金刚石参数选取、定制、加工和镀膜等方面都进行了全面尝试性实验。在连续光泵浦方面，我们观察到了Nd:YVO4激光晶体的连续激光和双自拉曼输出现象，双波长和多波长同时运转也已经成功实现，但是由于金刚石材料和加工工艺的限制，还暂时未获得很好的级联拉曼结果。通过跟不同的CVD钻石厂家进行合作，已经基本确立了目前能够获得最大增益的连续拉曼金刚石晶体的切割方向、角度，以及入射光的偏振与最大拉曼增益的匹配条件。对于金刚石晶体的抛光、镀膜等光学冷加工工艺有了全新的认识，对于项目中关键材料的制备和相关参数的设计有了新的理解。. 项目研究取得的理论和实验成果为后期基于金刚石拉曼激光和级联拉曼激光的研究提供了很好的理论参考和技术储备。