PROCEEDINGS ARTICLE | May 1, 2014
Proc. SPIE. 9135, Laser Sources and Applications II
KEYWORDS: Monochromatic aberrations, Mirrors, Laser vision correction, High power lasers, Reflectivity, Wavefronts, Deformable mirrors, Process control, Beam shaping, Error control coding
Compensation of low order aberrations is essential for high power solid state slab laser. With the increase of output
power, the peak-to-valley of wavefront distortion increase to dozens of micrometer. It’s difficult to control the wavefront
with deformable mirrors which always has limited stroke(<20μm). In this paper, a reflective beam shaping system is
designed to shaping the beam spot from rectangular to squarer. The beam shaping system consists of two x-oriented
cylindrical mirrors and two y-oriented cylindrical mirrors. Simulations of PID control algorithm for actively
compensating of low-order aberrations with reflective beam shaping system are presented. It shows that different
combinations of defocus, 0o astigmatism and 45° astigmatism, which is the main contributor of beam aberrations in slab
laser, can be well compensated by adjustment of distance and rotation angle of mirrors. And the convergence is fast when
the control error signal is set to a suitable combination of low order Zernike coefficients. For beam with wave aberrations
(PtV=82.6λ, RMS=18.2λ, Z4=23.6, Z5=7.1, Z6=19.6), the adjustment of distance between mirrors is below 100mm, and the rotation angle about z-axis is below 2 degree. The wavefront aberrations are decreased to a low level (PV=0.16λ,
RMS=0.04λ) which can be easily corrected later with DM.
