基于光纤锁模和固体再生混合放大的高功率、紧凑型飞秒激光器

Ultrafast optics is important frontiers in the fields of optics and lasers, and widely used in particle acceleration, attosecond science, micro/nano-fabrication, precision medicine, etc. Now, with the development of the laser technology, people have higher demands for output energy, repetition frequency, pulse duration, and compactness of ultrafast laser. A mechanism of hybrid fiber and solid-state amplifier system is proposed in this project to achieve high energy, high repetition rate laser output keeping miniaturization. Different from the reported all fiber or solid-state with laser amplification system, the respective advantage of optical fiber and the solid-state is combined in the project. The fiber lasers mode-locked as the front end produces a stable mode locked laser with an initial chirp. It is directly coupled into a LD pumped regenerative amplifier based on Yb:CaF2 crystal. In the regenerative amplifier, the dissipative Self-phase Modulation (SPM) effect and folded cavity structure are proposed to avoid the nonlinear chirp induced by SPM effect, and improve the compactness of regenerative amplifier further. The amplified laser pulse is recompressed by a grating compressor and achieving hundred kHz、hundred uJ、 hundred femtosecond order laser output. The applications of high- energy, and high-frequency miniaturized femtosecond laser in scientific and industrial applications will be significantly benefited from this research project.

超快激光技术是光学与激光领域的重大前沿，在粒子加速、阿秒科学、微纳加工、精准医疗等方向都有广阔的应用前景。当前，人们对超快激光的输出能量、重复频率、脉冲宽度以及紧凑性提出了更高的要求。本项目提出一种基于光纤锁模结合固体再生混合放大获得高能量高重频的小型化飞秒激光源。区别于文献报道的全光纤或者全固体激光放大的方法，该项目结合了光纤和固体两种增益介质的优势，利用紧凑的光纤锁模激光器作为前端输出，提供稳定的、带有预啁啾的种子光。利用半导体泵浦的基于Yb:CaF2晶体的固体再生放大器对种子光进行放大。再生放大器中利用耗散自相位调制效应和折叠腔结构来避免自相位调制引入非线性啁啾，进一步提高再生放大器的紧凑性。放大后的激光脉冲经过光栅压缩后实现百kHz、百微焦、百飞秒量级的激光输出。该项目研究对高能量、高重频、小型化飞秒激光器在科研和工业中的应用有重要意义。

飞秒激光由于具有脉冲宽度窄、峰值功率高的特点，使得飞秒激光已经广泛应用在基础研究、工业加工、以及生物医疗等众多领域。目前，实现飞秒激光输出的主要增益介质是光纤和以块状或者薄片为代表的增益晶体。基于光纤的飞秒激光器由于具有结构紧凑、无需准直、环境不敏感等优势已经得到了迅速地发展。然而，受限于光纤纤芯导致的非线性效应、材料损伤等因素，当光纤飞秒激光器输出的脉冲能量通常达到微焦量级时，脉冲的时域质量会受到严重影响。与此同时，由于其大的储能体积，使得固体放大技术非常适用于获得高脉冲能量的场合。因此，本项目将光纤飞秒激光器作为种子光，同时利用块状晶体作为放大器，结合了两种增益介质的优点，实现高质量、高能量的飞秒激光脉冲输出，同时对飞秒激光的波长进行频率变换，拓展飞秒激光的应用领域。主要对以下三个方面进行了研究：（1）.基于光纤锁模和固体再生混合放大的高能量、紧凑型飞秒系统，实现输出压缩前30 μJ,60 kHz的能量输出，压缩后脉冲宽度270 fs,能量21 μJ。（2）.基于非线性晶体，开展紫外及深紫外超快激光器的研究，实现了1 MHz,皮秒213 nm国际最高功率的输出。（3）.基于飞秒激光器和折叠激光腔搭建超紧凑、高重频OPO激光器，实现了最高重复频率3 GHz且波长可调谐的飞秒激光脉冲输出。综上所述，本项目成功开展了一系列的理论和实践研究，为利用高能量飞秒激光器的研究与应用提供了详细和科学的研究资料。项目资助相关成果已发表在国际权威SCI期刊杂志，并申请相关专利。