Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) has made a new progress in the dispersion management for a 100PW level laser, based on the mismatched-grating compressor. The relevant result is recently published on High Power Laser Science and Engineering on November 8, 2022.

In 1997, Kane and Squier firstly proposed the mismatched-grating compressor, which has an extra variable parameter (the grating groove density), compared with the conventional Treacy compressor. By mismatching the grating pair separation and the incident angle in stretcher and compressor, the second- and third-order dispersion (GDD and TOD) can be exactly compensated respectively.

While, by mismatching the grating groove density in stretcher and compressor, the fourth-order dispersion (FOD) can be nearly cancelled out. In other words, GDD, TOD and FOD can be simultaneously compensated and hence near FTL compressed pulses can be achieved, by using mismatched-grating compressor.

However, the previous two PW level femtosecond lasers based on mismatched-grating compressor did not obtain good experimental results. The compressed pulse durations are only ~30 fs, which are far from the FTL. This is mainly limited by the commercial available gratings of that time, and the gratings adopted in above PW lasers were not equipped with the optimal groove density.

Fortunately, the gratings with arbitrary groove density are customizable nowadays, benefitting from the development of gratings manufacturing technique. Hence, the mismatched-grating compressor possess the potential for good dispersion management. However, as a kind of passive dispersion management method, the feasibility of mismatched-grating compressor in practical application is still uncertain.

In this work, our research team fully studied the dispersion characteristics of mismatched-grating compressor and proved its advantage in the dispersion management for a 100PW laser theoretically. The numerical results indicate that the mismatched-grating compressor based SEL-100PW laser (chirped pulse duration ~4 ns, spectral bandwidth ~210 nm) can realize <13fs near-FTL pulses.

In addition, we also comprehensively study the tolerance of mismatched-grating compressor. Including the tolerance to the calibration error of the stretcher, the tolerance to the grating groove density error, and the tolerance to the material dispersion error in system.

The numerical results effectively clarify that good tolerances and near FTL pulse duration can be achieved simultaneously by keeping a balance among the residual GDD, TOD and FOD in the laser system.

More importantly, the good tolerances of mismatched-grating compressor offer an important support for its practical application and meaningful guidance for the design and manufacture of 100PW laser.

Fig.1 (a) Simulated pulse spectrum and calculated spectral phase (b) FTL and corresponding compressed pulses of SEL-100 PW laser facility. (Image by SIOM)

Fig.2 The pulse durations (a) and its partial projection (b) after balancing the residual dispersion by optimizing compressor, when the grating groove density in stretcher and the material dispersion in laser system are changing simultaneously. (Image by SIOM)

Article website:
https://doi.org/10.1017/hpl.2022.29

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/