This paper describes the use of closed-loop adaptive optical system to improve the focusing of femtosecond laser beam. Our adaptive system corrects for the low-order aberrations of laser. But even if the aberrations of the laser beam are compensated the focal spot obtained with parabolic mirror is still far from ideal one. And the reason is the aberrations of the parabolic mirror and its poor adjustment. Comparison of phase-conjugate and multi-dither algorithms to correct for the parabolic mirror aberrations is presented. The principle of proper adjustment of the parabolic mirror based on M2 minimization is shown.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.