光学超晶格非线性镜锁模2μm波段激光器

Ultra-fast Laser light sources in the 2-micron spectral range have attracted increasing attentions and research interests due to the applications in areas such as industry machining, time-resolved spectroscopy, nonlinear frequency conversions, optical communication and photo-medicine et. al. The commonly-used way to obtain 2-micron laser light is to combine Tm3+、Ho3+-doped as well as co-doped laser gain mediums with techniques such as saturable mirror mode-locking and second-order nonlinearity mode-locking. Among these, nonlinear mirror mode-locking using optical superlattice utilizes nonlinear process to modulate amplitudes and phases of the interacting waves, and has the advantages of large modulation depth, wide wavelength range, fast response time, high damage threshold, high integration and flexible design, which makes it a new route for realizing high-performance mode-locked lasers. In the proposed project, the nonlinear mirror mode-locking technique is used to realize mode-locked lasers around 2-micron. We will evalute the intra-cavity frequency doubling characteristics and the response in the pico-second time domain of optical superlattice, and will seek the optimized domain structure using quasi-phase-matching theory as well as micro-structure design method. By this means, the parameters for high-performance mode-locking can be obtained thus for realizing high-efficient and stable mode-locked laser output around 2-micron.

2μm波段的超快激光在工业加工、时间分辨光谱学、非线性频率转换、光通信和光医学等方面有着重要的应用，正引起人们越来越多的关注和研究兴趣。该波段的超短脉冲输出，可以使用掺Tm3+、Ho3+离子（包括共掺）的激光增益介质结合可饱和吸收体锁模、二阶非线性锁模等技术获得。其中，基于光学超晶格的非线性镜锁模技术是获取高性能锁模激光的一条新途径，具有适用波长范围广、调制深度大、时间响应快，抗损伤阈值高、设计灵活和集成度高的优点，其本质是利用非线性过程调制光的强度和相位。本项目拟使用Tm:YAP结合超晶格非线性镜锁模实现2μm波段皮秒激光输出，评价光学超晶格在中红外波段的腔内倍频性能和皮秒时域的响应特征；研究畴结构对基波和倍频波强度、相位的调制，根据准相位匹配和微结构设计的原理探索超晶格锁模的最优化畴结构，从而对锁模参数进行优化和调整；获得高效、稳定的2μm波段锁模激光。

全固态的2um波段锁模超快激光光源在光医学、遥感、光通讯、时间分辨分子光谱学等领域有重要的应用前景。结合我们在光学超晶格全固态激光器方面的工作积累，特别是前期在近红外波段光学超晶格锁模激光器方面的研究进展，我们在本项目中成功研制了基于级联二阶非线性效应的光学超晶格2um波段全固态激光光源。我们发展了优化的室温电场极化技术，即使用金属液体混合电极配合质子交换技术，制备出了光学质量均匀，占空比合适的高质量铌酸锂光学超晶格。用周期极化铌酸锂光学超晶格作为非线性晶体，结合全固态激光技术，我们搭建了1988nm的全固态光学超晶格锁模激光器。输出功率达到瓦级，脉冲宽度为几个皮秒，重复频率97MHz。我们的方案为2um波段锁模激光器这一被广泛关注，且有挑战性的课题提出了新的额外的解决方法；同时丰富了光学超晶格在激光技术方面的应用内容。