Proceedings Article | 26 April 2019
Proc. SPIE. 11034, Short-pulse High-energy Lasers and Ultrafast Optical Technologies
KEYWORDS: Photovoltaics, Pulsed laser operation, Laser systems engineering, Spatial filters, Manufacturing, Chromatic aberrations, Diffraction gratings, Wavefront distortions, Femtosecond phenomena, Mirrors
To ensure a high signal to noise contrast ratio, lots of challengeable work must be done during the construction of a petawatt level laser system. In this report, we analyse the effects on the contrast ratio by the optical element manufacture errors expressed as the peak-valley value (PV value) and the PV gradient value, the chromatic aberration and group delay in system design. Using the Fourier transformation method with the random phase attached on the laser beam in frequency domain, it is proved that for manufacture errors, PV gradient value is more tolerable than that of PV value. At the terminal end of a petawatt level laser system, there exist, in pulse compressor, spectral clip, grating manufacture errors and non-uniformity of the diffraction efficiency that will affect the final SN contrast ratio of the laser system. Since the spectral clip here is soft that can benefit the promotion of the contrast ratio. But for manufacture errors of the large size grating, when PV = 1/5 wavelength, and PV differential gradient about 1/75 wavelength per centimeter. The terminal SN contrast ratio is restrained. When focused on the target, simulation for SN contrast ratio near the focal region caused by the residual distortion is taken. Calculation shows that, for a 20 microns focal spot, to maintain the 108:1 contrast ratio across the whole focal spot, residual wavefront distortion should be compensated to PV value less than 0.2 wavelength.
