无序钨钼酸盐晶体自拉曼锁模激光的研究

As the development of laser has been a tendency into small and low-lost, self-raman crystal, as a new efficient methord to obtain raman laser, replaced the combination of laser and raman crystals. Due to the pulse-compression effect caused by raman conversion, self-raman mode-locked laser becomes a new way for ultrafast laser. Recently, the pulse width of ultrafast laser produced by self-raman mode-locked laser is very limited, that's why narrowing down laser pulse width of ultrafast laser and broadening on wavelength range have become one of focuses in research of ultrafast laser. This project use disordered tungstate and molybdate laser crystal to obtain ultrafast laser with ultrashort even attosecond pulse width. Due to inhomogeneous broadening caused by disordered phase, spectra of stimulated emission and Stimulated Raman Scattering are quitely wide. What’s more, the third-order nonlinear optical coefficient of these kind of crystals are much higher than those of Raman crystals, which make disordered tungstate and molybdate laser crystal become more conducive to obtain self-Raman mode-locked laser performance. We will research the effection caused by the interaction between thermol lens and Kell lens effections. The differences of frequency and spatial profile of modes were determined by the observation of spatial-temporal performance and dynamics. Since there are no more other optical components in self-Raman mode-locked laser resonant cavity, it will greatly reduce the loss of cavity and improve the stability. We expect to find a route to realize the stable self-Raman mode-locked laser. These researches will bring much benefit for the miniaturization and commercialization of ultrafast laser.

随着激光器向小型化和低损耗方向的发展，用自拉曼晶体取代增益介质和拉曼晶体的组合，已逐渐成为拉曼变频的主要发展方向。由于自拉曼激光的脉宽压缩效应，使自拉曼锁模技术成为产生超快激光的新机制，也拓宽了超快激光的波长范围。现阶段自拉曼锁模产生超快激光的脉宽有限，而超短脉冲激光正进行着从飞秒向阿秒跨越，所以压窄脉宽成为当前超快激光研究的焦点。本项目使用无序结构的钨钼酸盐晶体作为自拉曼介质，由于其谱线非均匀展宽，且三阶非线性系数较大，能够获得可调谐自拉曼激光。在自拉曼激光的宽谱线作用下，通过自拉曼锁模技术，可直接获得超短脉宽激光输出。通过分析热透镜和克尔透镜效应间的相互作用对锁模激光性能的影响，重点研究腔内光场的时间-空间的动力学过程，探究自拉曼激光模式锁定机制，据此探索一条获得结构紧凑、性能稳定、脉宽超窄、损耗低的锁模激光的有效技术途径，为超快激光的小型化和商业化提供基础。

无序相位结构的钨钼酸盐晶体，其拉曼增益线宽受非均匀加宽影响，较目前报道的自拉曼晶体宽很多，因此在拉曼脉宽压窄效应基础上，可直接获得脉宽更短且性能更优异的自拉曼锁模激光。本项目主要研究了两倍无序钨钼酸盐激光晶体的受激吸收、发射、拉曼光谱以及基频激光、自拉曼激光性能，通过理论模拟计算和实验研究，开展此类无序晶体在可调谐自拉曼激光产生过程中的动力学研究。LD泵浦 Nd: LiGd(WO4)2晶体获得了从1057 nm – 1061 nm的多波长激光同时输出：在自由运转模式下最大输出功率0.63W，斜效率40.6%；在调Q模式下，最大输出功率0.43W，斜效率30.2%；光束质量M2因子为M2x =2.73，M2y=2.12. LD泵浦Nd:LiLa(MoO4)2晶体得到了1061 nm 和 1060 nm双波长激光输出，最大激光381 mW，斜效率14.5%。在基频激光的研究基础上完成了两种晶体的拉曼光谱特性研究，通过自拉曼激光热效应的影响因素，推导获得了热焦距公式，综合考虑改善热效应和提高拉曼转换效率，设计谐振腔参数。但是在实验过程中，由于晶体质量欠佳，自拉曼激光输出时出现断裂，未能测试得到较好的实验结果。本项目理论研究了自锁模激光器稳定运转及自启动的条件、单增益介质的自锁模自受激拉曼效应激光动力学过程。.本项目对钕离子掺杂的两倍无序钨钼酸盐激光晶体的高效基频激光的实验的研究，以及自拉曼激光热效应的研究，提升了此类晶体在可调谐自拉曼激光的应用。尽管受晶体质量影响，相信通过技术提升，在高晶体质量的保证下可以获得高效的自拉曼激光锁模超快激光输出，为超快激光的小型化提供新的途径。