Phase correction of laser radiation with the use of adaptive optical systems at the Russian Federal Nuclear Center—Institute of Experimental Physics

Abstract

Results obtained at the Institute of Laser Physics Research (which is part of the Russian Federal Nuclear Center — Institute of Experimental Physics) on phase correction of pulsed and continuous wave laser radiation by closed-loop adaptive optical systems (AOS) with flexible deformable mirrors are described. With the help of a conventional AOS including a Hartmann-Shack wavefront sensor and an adaptive mirror having a 220 × 220 mm aperture, aberrations of the beam of a powerful pulsed laser facility called Luch have been reduced by an order of magnitude. The development of special software for reconstruction of singular wavefronts by the Hartmann-Shack sensor has allowed us to perform the correction of a doughnut-shaped Laguerre-Gaussian vortex laser beam in an AOS with a bimorph mirror and to focus it into a bright axial spot that drastically increases the Strehl ratio. Adaptive optical systems have been developed where the adaptive mirror control is ensured by searching for an extremum of a chosen criterion functional with the help of a stochastic parallel gradient algorithm rather than by means of wavefront measurements. Embedding of microcontrollers into the control unit has allowed us to reach an AOS bandwidth of 5 kHz and to demonstrate the dynamic phase correction of tip-tilts and higher aberrations of the wavefront caused by turbulence induced by heating of the beam propagation path under laboratory conditions.