Bulk Damage Threshold Research Articles

Investigation of the optical strength of KRS-6 and KRS-5 crystals subjected to pulsed CO2laser radiation

The influence of the composition of the atmosphere in which KRS-6 crystals were grown on their spectral transmission, light scattering, and optical strength when subjected to pulsed CO2 laser radiation was studied. The bulk damage threshold of KRS-6 at 10.6 μ wavelength was shown to be directly related to the transmission and scattering of light in the visible part of the spectrum and the damage threshold of KRS-6 increased on reduction of the sulfur content in the specimens. A study was made of the influence on the surface damage threshold of the type of polishing abrasive used, and it was shown that the best results were obtained using diamond pastes and powders.

Influence of adsorbed water on the optical strength of infrared optics elements

Spectroscopic and mass-spectroscopic methods were used in an investigation of the composition of the substances ejected from the surfaces of polished transparent infrared materials acted upon by CO2 laser pulses. The main components were found to be water, hydroxyl groups, and original material. A preliminary laser cleaning procedure reduced the amount of ejected water and hydroxyl groups, and also increased the surface breakdown threshold. The threshold of a surface free of an adsorbed water layer (for example a surface cleaved in vacuum) was equal to the bulk damage threshold of the material being investigated. The dynamics of the breakdown plasma formed near the surface was investigated and its temperature was measured. An analysis was made of possible ways of increasing the surface damage threshold of infrared optics elements by reducing the adsorptivity of the surface. The example of NaCl was used to demonstrate that chemical etching of a mechanically polished surface produced a short-term (5 min) increase in the breakdown threshold by a factor of 5–6 and a long-term (at least 3 months) increase by a factor of 2.5–3.

Appearance of opacity and damage of optical materials by carbon dioxide laser pulses

The thresholds of the appearance of opacity and damage in the bulk and on the surface of some materials used in the infrared range were determined. A laser cleaning effect was observed for materials whose surface optical strength exceeded the breakdown threshold of air near the surface. This made it possible to raise the opacity threshold to the bulk damage threshold. The opacity threshold of such a cleaned surface fell as a result of adsorption of contaminants from air.