​Laser properties of sapphire crystals (4)

Laser properties of sapphire crystals (4)

In general, bulk damage in ruby occurs at radiant energy densities above 0.7 J/cm2 due to radiation absorption or self-focusing of radiation by inclusions and other absorbing defects. Most of this energy is absorbed by Cr4+ Ion and impurity absorption, some of Cr4+ ions and impurities change their phase state under irradiation. The phase volume also changes, resulting in additional volume stress. In addition to passive absorption, some impurities (such as Mg2+) when the pulse number increases reduce the output energy. Under strong excitation, titanium impurities cause stable color center (CC) formation and reduce bulk intensity.

Bulk intensity may also be reduced due to initial or pump-induced RE optical inhomogeneities, resulting in non-uniform energy distribution at element intersections and damage in regions subject to the strongest radiation. High-energy lasers either use highly homogeneous rubies (by Czochralski method growth) or use an optical design in which the laser beam is repeatedly passed through different regions of the activated body during the generation process.

The effect of the pores on the bulk strength is not very large. Obviously, the region containing the pores does not participate in the generation process and has a low local energy density.

The bulk damage may produce the destruction of the crystal end face. For the pulse energy of 0.2J and tp = 30-70 ns, the first Fresnel diffraction zui value may be prone to surface damage at the position of 8-10 mm from the end face at the edge of the bulk damage region.

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