基于光学超晶格非线性镜锁模的全固态可调谐超快激光器研究

All-solid-state wavelength-tunable ultrafast laser sources in the 1μm spectral range are widely applied in fields of military, medicine et. al. The commonly-used way to obtain this type of laser sources is to combine techniques of mode-locking (Semiconductor saturable absorption mirrors, carbon nanotubes and graphene) with wavelength modulating. Nonlinear mirror mode-locking based on optical superlattices has many advantages such as: wide wavelength range, large modulation depth and high damage threshold, which makes it a new route for realizing high-performance tunable ultrafast laser. In the proposed project, the Yb3+-doped laser gain medium combined with the nonlinear mirror mode-locking is used to realize tunable ultrafast laser. The optimized domain structure obtained by using quasi-phase-matching as well as micro-structure design method will be sought for. The interaction of light and matter, the operating mechanism of nonlinear mirror mode-locking and wavelength tunability will be studied. Finally a tunable all-solid-state ultrafast laser around 1μm will be obtained.

1μm波段全固态、可调谐超快激光器在军事、医学等领域有着广泛应用，目前通常由可饱和吸收镜、碳纳米管、石墨烯锁模结合波长调制技术产生。基于光学超晶格的非线性镜锁模技术具有适用波长范围广、时间响应快、损伤阈值高等特点，是获得可调谐超快激光的一条新途径。本项目拟使用掺镱激光增益介质及超晶格非线性镜锁模技术，实现可调谐超快激光。根据准位相匹配和微结构设计原理探索最优化超晶格结构；分析光与物质的互作用过程，掌握非线性镜锁模的运行机制；研究激光波长的调谐规律，最终获得1μm波段全固态、可调谐超快激光器。

利用光学超晶格的二阶及三阶非线性效应，我们获得了宽带飞秒超连续光谱，研究了飞秒激光与晶体的相互作用导致的成丝现象和切伦科夫锥形辐射，计算了光丝内的非线性折射率；基于光学超晶格非线性镜，获得了1μm波段亮脉冲和暗脉冲，研究了暗脉冲调制深度与泵浦功率、晶体温度的变化关系。具体如下：.利用周期极化钽酸锂光学超晶格，以800nm飞秒激光为入射光，获得了飞秒超连续光谱，光谱范围分为两个波段，其中490-970nm为三阶非线性导致的光谱展宽，380-440nm 为展宽光谱的进一步倍频产生。利用超连续光谱的切伦科夫辐射理论研究了飞秒激光与晶体的相互作用导致的成丝现象和切伦科夫锥形辐射，产生的切伦科夫锥形辐射角随波长的增加而减小，计算了光丝内的非线性折射率为0.024，与质子交换光波导的的折射率改变为同一数量级。. 基于光学超晶格非线性镜获得了1μm波段亮脉冲和暗脉冲。研究了暗脉冲重复频率随波矢失配量的变化关系，获得暗脉冲最大调制深度为22.3%，通过调谐光学超晶格温度在较宽的温度范围内均可获得暗脉冲，并研究了暗脉冲调制深度随晶体温度的变化关系。通过调节光学超晶格，获得暗脉冲最小宽度为109 µs。. 研究结果表明光学超晶格获得的飞秒超连续光谱可以应用于宽调谐白光光源的产生等领域；而暗脉冲激光在光波导传输中噪声比亮脉冲小，损耗少，因此在信号处理和光纤通信方面有很大的应用前景。