When irradiated by a low fluence IR laser radiation, a PMMA plate becomes mat. The damage results from the in-depth absorption of the laser light, which yields a microscopic boiling process. The aspect of the trapped bubbles shows the importance of the absorption depth, which varies with the lasers taken into account (CO2 , DF and HF). The threshold of this boiling process has been measured as a function of the incident power density for the three lasers considered. The behaviour is conduction-dominated in the case of the CO2 laser radiation and absorption-dominated in the case of the DF and HF laser radiations.
The design, construction and operational characteristics of an arc driven supersonic cw HF chemical laser of more than I kW power, which has been developed for laser-material investigations, are presented. Overtone lasing has also been obtained with a power of 220 W.
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