Correction of vortex laser beam in a closed-loop adaptive system with bimorph mirror.

The phase correction of a vortex laser beam is undertaken in the closed-loop adaptive system including a Hartmann-Shack wavefront sensor with singular reconstruction technique and a bimorph piezoceramic mirror. After correction the vortex doughnutlike beam is focused into a beam with bright axial spot that considerably increases the Strehl ratio and optical system resolution. Since the phase break cannot be exactly reproduced on the flexible mirror surface, off-axis vortices appear in the far field at the beam periphery.

Analysis of algorithms for adaptive control of laser beams in a nonlinear medium.

Adaptive correction for thermal blooming by multidither and phase-conjugation algorithms is analyzed with the use of numerical models of beams propagating in a nonlinear medium. Methods to increase the stability of these algorithms are proposed. The influence of an adaptive mirror on the efficiency and the divergence of correction algorithms is considered.

Wavefront reconstruction of an optical vortex by a Hartmann-Shack sensor.

Reconstruction the phase front of a vortex laser beam is conducted by use of a Hartmann-Shack wavefront sensor. The vortex beam in the form of the Laguerre-Gaussian LG(0)(1) mode is generated with the help of a spiral phase plate. The new reconstruction technique based on measured wavefront gradients allows one to restore the singular phase surface with good accuracy, whereas the conventional least-squares approach fails.