Ultra-fast petawatt-class laser systems have undergone rapid development by the incorporation of chirped-pulse amplification (CPA) and optical parametric chirped-pulse amplification (OPCPA) technologies. In October 2018, Shanghai Super-intense Ultrafast Laser Facility (SULF) achieved the amplified output energy of 339J, which support the peak power of 10.3 PW. For the high-field laser- matter interaction research, the focal intensity at the target is a critical parameter. Therefore, in addition to increasing the pulse energy and shortening the pulse duration, decreasing the size of the focus spot has become another essential and economic method to increase the intensity.

    Given the complex optical elements and severe aberrations of petawatt laser systems, double or more adaptive optics systems (AOSs) with cascaded correction have been required in high-power laser systems to improve the focusing ability of the laser pulse. Recently, an experimental scheme, based on the function of double deformable mirrors (DMs) in the AOSs, was developed by State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (CAS), and it has succeeded in the compensation of the wavefront aberrations of the laser beam.

    The major part of the large-scale aberrations was compensated by the 300mm-DM with a large stroke in the second AOS and the small-scale residual aberrations were further improved by the high-spatial-resolution 130mm-DM in the first AOS. Focused with an f/2.5 off-axis parabolic mirror (OAP), a focal spot close to the diffraction limit was achieved, which contained approximately 27.69% energy in the full width at half-maximum (FWHM) area  (2.75 × 2.87 um²). A peak intensity of 2 × 10²² W/cm² was also realized at the output of 5.4 PW, and it could exceed 10²³ W/cm² in the SULF 10 PW laser facility using an f/1.8 OAP. The focal intensity improvement will be implanted at peak power of 10 PW very shortly.

    The results, entitled "Improvement of the focusing ability by double deformable mirrors for 10-PW-level Ti: sapphire chirped pulse amplification laser system", were published in Opt. Express (vol. 26, Issue 20, pp. 26776-26786 (2018)).

The phase profiles of the focal spots (a) before and (c) after the correction; (b) and (d) the corresponding focal spots focused (Image by SIOM)

Contact:

Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: caoyong@siom.ac.cn