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.

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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.

A kinetic model of the working medium of a discharge excilamp on the B-X transition of mercury bromide, HgBr, excimer molecules has been proposed. The model explains the nonmonotonic dependence of the excilamp radiation intensity on the partial pressure of mercury dibromide molecules by the attachment of electrons to these molecules. HgBr(X) molecules were found to transit into the HgBr(B) excited state due to their collisions with high-energy electrons, thereby improving the excilamp characteristics. K e y w o r d s: excilamp, gas discharge plasma, kinetics, excimer radiation, mercury halides.

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