Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS) has made new progress in the dispersion control of ultra-broadband petawatt (PW) - level optical parametric chirped pulse amplification (OPCPA) systems, implementing a combination of double-grating Offner stretcher and Treacy compressor, which is the first time to the best of their knowledge. The relevant result is recently published on Optics & Laser Technology on December 20, 2021.

The single-grating Offner stretcher is not really aberration-free, due to its incident grating having to deviate from the center of the curvature of spherical mirrors to expand the pulses temporally. Thus, there is an evitable dispersion mismatch between the single-grating Offner stretcher and its conjugated Treacy compressor, regardless of whether there is material dispersion or not. And extra dispersion control methods are usually necessary for the single-grating Offner stretcher based high-peak-power laser systems.

Different from a single-grating Offner stretcher, the double-grating Offner stretcher is truly aberration-free. The aberration-free characteristic endows double-grating Offner stretcher with the advantages of good beam quality and perfect-dispersion-match with conjugated Treacy compressor and hence makes it an ideal pulse stretcher for OPCPA systems, in which the low material dispersion induced dispersion mismatch between the stretcher and the compressor is slight. Though the aberration-free characteristic of the double-grating Offner stretcher is well known, its superiority for dispersion control in OPCPA systems is still unexplored.

In this work, the research team focused on the dispersion control in PW level OPCPA systems by the use of a double-grating Offner stretcher. The numerical results indicate that near FTL pulses can be achieved in double-grating Offner stretcher based broadband OPCPA systems with peak power up to PW level. Moreover, in a proof-of-principle experiment under relatively low laser peak power, amplified pulses with 3 ns chirped pulse duration and 210 nm spectral bandwidth are compressed to 15.4fs (FTL value is 15fs) just based on the combination of a double-grating Offner stretcher and a Treacy compressor.

The researchers said that it is the broadest amplified spectrum (210 nm) and shortest compressed pulse duration (~15 fs) achieved in existing OPCPA systems.

Fig. 1. Measured spectrum (red line) of amplified pulses, (b) FTL (black dot), measured spectral phase (blue line) and pulse duration (red line) of compressed pulses. (Image by SIOM)

Article website:
https://doi.org/10.1016/j.optlastec.2021.107791

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/