Surface and volume scattering, surface-damage, and optical homogeneity studies of ruby crystals and their connection with laser-emission characteristics

Results of our investigation of the optical homogeneity of ruby crystals and its relation to the main laser-emission characteristics (i.e., beam divergence, far-field intensity distribution, energy output, and spectra of modes) are described. Good correlation has been found between the laser characteristics and the optical properties of the investigated ruby samples. On the basis of the experimental data, the different sources of the optical inhomogeneity of the ruby crystals grown by the Verneuil method and their influence on the laser characteristics are analyzed. It is shown, in particular, that internal mechanical strains have the most injurious effect on the beam divergence, the intensity distribution, and the mode-selection conditions. It is found that a volume light scattering contribution in laser energy losses is, to a large extent, due to the Rayleigh component of scattering. Laser-produced surface-damage experiments with ruby and sapphire crystals are also described. A variable pulse duration between
1-400 \mu
s under normal laser operation and 30-ns Q-switched pulsed laser operation have been employed in these experiments. Optical and structural surface properties and their effect on a surface-damage threshold have been studied and the mechanism of laser-produced surface damage is discussed.