Recently, the research team of the State Key Laboratory of Intense Field Laser Physics, Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences has made new progress in the research of dispersion control of 100PW laser systems. The relevant achievements were published in High Power Laser Science and Engineering under the title of "Displacement management for a 100 PW level laser using a mismatched grating compressor".
As early as 1997, Kane and Squier proposed the unmatched grating compressor. Different from the traditional Treacy compressor, the unmatched grating compressor introduces an additional variable parameter - grating reticle density. The second order dispersion (GDD) and the third order dispersion (TOD) can be compensated by optimizing the mismatch of grating pair spacing and incidence angle in the stretcher compressor; The fourth order dispersion (FOD) can be compensated by optimizing the mismatch of grating groove density in the stretcher compressor. Therefore, the unmatched grating compressor can realize the simultaneous compensation of GDD, TOD and FOD, so as to obtain the compression pulse with near Fourier transform limit (FTL). However, the previous experimental results of two PW class femtosecond lasers based on unmatched grating compressors are not ideal. The compression pulse width is only~30 fs, which is far from the FTL value. This is mainly due to the limitation of the grating types at that time. The gratings used in the above two lasers were not equipped with the optimal reticle density. With the development of grating manufacturing technology, gratings with arbitrary groove density can be customized at present, which also makes unmatched grating compressors have good dispersion management potential. However, as a passive dispersion management method, the feasibility of unmatched grating compressor in practical application is still uncertain.
The research team has fully studied the dispersion characteristics of the unmatched grating compressor, and theoretically proved its dispersion control advantages in the 100PW laser system. The numerical results show that the SEL-100 PW laser system based on unmatched grating compressor (chirped pulse duration~4 ns, spectral bandwidth~210 nm) can achieve near FTL compression pulse less than 13 fs. In addition, the research team also comprehensively and deeply studied the tolerance of unmatched grating compressor, including: the tolerance of stretcher calibration error, the tolerance of grating reticle density error, and the tolerance of material dispersion error in the laser system. Numerical results show that by balancing the residual GDD, TOD and FOD in the laser system, the unmatched grating compressor can achieve good tolerance in the above three aspects, and achieve near FTL compressed pulse output. This work proves the good tolerance of the unmatched grating compressor, which provides an important support for its practical application, and provides meaningful guidance for the design and manufacture of 100PW laser.
Figure 1. Numerical simulation of 100PW laser amplification spectrum and output pulse based on unmatched grating compressor.
Figure 2. Output pulse width (a) and tolerance (b) based on unmatched grating compressor when there are errors in both material dispersion and grating groove density.
Relevant work has been supported by the national key research and development plan, the strategic leading science and technology project of the Chinese Academy of Sciences, and the major science and technology project of Shanghai.
Related links: http://dx.doi.org/10.1017/hpl.2022.29
From: Guangxingtianxia and Shanghai Institute of Optics and Mechanics
