Far-field description methods for high power ultra-short pulse laser

Using statistical methods and numerical simulation, the far-field description methods for high power ultra-short pulse laser were established. The results show that the percentage of energy in FWHM of the ideal super-Gaussion beam is no more than 70%, and it reduces with the order of the super-Gaussian beam increasing. The FWHM of focus will keep a constant when beam quality was good, and the power density in FWHM has no relationship with FWHM, whereas, it has a linear relationship with Strehl ratio and percentage of energy in FWHM. Therefore, the paper points out that FWHM of focus or severalfold diffraction limits cannot be simply used in giving the peak power density. Strehl ratio or the encircled energy within FWHM is more appropriate.