High-power ultrafast laser sources are highly demanded in various scientific research and industrial applications. The high peak power enables these applications to be driven, while the high average power satisfies their need for high photon flux and high signal-to-noise ratio. The Yb-based CPA laser system can reach several hundred watts, and even >1 kW, thanks to the high quantum and Stokes efficiency, as well as the excellent thermal management of state-of-the-art fiber, thin-disk, and Innoslab laser architectures. Although the fiber laser cannot achieve high pulse energy output due to the smaller aperture, but it can work as an outstanding frontend owing to its robustness, excellent beam quality, and the integration of chirped fiber Bragg gratings (CFBGs) as the stretcher without misaligning like the grating stretcher. The solid-state amplifiers shine in terms of high pulse energy owing to negligible nonlinear effect and high damage threshold of critical devices, especially the Innoslab amplifier endowed with the compact configuration and high amplification factor. Hence, the Innoslab amplifier seeded by a fiber frontend provides an attractive choice for achieving a superior high-power laser system. However, there are still some drawbacks that cannot be ignored. First, the narrow gain bandwidth limits the generation of sub-100 fs ultrashort pulses, which is a common drawback of Yb-based lasers. Second, the compressed pulses always show the obvious pedestals which can be attributed to the inability of grating compressor in offsetting the higher-order dispersion mainly from fiber frontend. Finally, the output beam of Innoslab amplifier is always elliptical and accompanied with spatial distortion even after the state-of-the-art reshaping and spatial filtering.

The research group from Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, demonstrates an economical post-compression with multi-thin-solid-plates to mitigate the limitation of the Innoslab amplifier seeded by a fiber frontend. The article was published in High Power Laser Science and Engineering, vol. 12, Issue 4 (Zichen Gao, Jie Guo, Yongxi Gao, Yuguang Huang, Zhihua Tu, Xiaoyan Liang, "Efficient dual-stage all-solid-state post-compression for 100 W level ultrafast lasers," High Power Laser Sci. Eng. 12, 04000e45 (2024)) . Not only >8-fold pulse compression with 94% transmission is achieved, the pulse quality and spatial mode are also improved, enabling a high-power ultrafast laser source with 64 fs pulse duration, 96 W average power at 175 kHz repetition rates, and good beam quality.

Fig.1 Schematic of experimental setup. The high-power ultrafast laser output is achieved by the dual-stage all-solid-state post-compression (blue shaded) driven by a >100W average power Yb:YAG Innoslab amplifier system (yellow shaded).

The nonlinear spectral broadening in this post-compression scheme relies on a dual-stage thin fused silica plates, which is periodically placed to balance the diffraction and self-focusing effect. The stable mode propagation is achieved to suppress the spatio-temp coupling effect for high transmission and good beam quality. In addition, this post-compression scheme has special advantages on the Innoslab amplifier seeded by a fiber frontend. In time domain, the final pulses are almost pedestal-free and quite close to Fourier-transform-limited (FTL) pulse duration, because the compensation for high-order dispersion during the nonlinear process. In space domain, the increasingly circular and clean beam profile can be attributed to spatial mode self-cleaning effect. Similar phenomenon was observed in the nonlinear process of filamentation, self-focusing collapse and multimode fibers, which was considered as the effort of spatial self-organization of laser beam.

Fig. 2 Measured and Lorentz fitted autocorrelation traces of CPA output, first-stage and second-stage post compression.

Fig. 3 Evolution of beam quality and beam profile at different locations with the output power.

This work indicates that the periodically placed thin-solid-plates post-compression is an efficient and economical complement for the Innoslab laser system and this robust and compact combination may be a promising scheme for the high-power ultrafast laser. In the future, this post-compression scheme will be used for generating the few-cycle lasers with higher power, supporting more applications and outstanding performance.