Large-spot thermal coupling of CO2 laser radiation to metallic surfaces

Abstract

Thermal coupling of pulsed 10.6-μm laser radiation to aluminum and titanium targets was measured as a function of incident fluence, focal-spot size, and ambient pressure. Thermal coupling coefficients were measured with both calorimetric and fast-response surface-thermocouple techniques. Thermal coupling coefficients of over 0.3 were observed with the onset of a well-developed plasma at the target surface. The thermal coupling was observed to increase slightly with increasing irradiated spot size and to decrease monotonically with increasing laser fluence. Under conditions of low ambient pressure (∼0.5 Torr) the breakdown threshold was increased by a factor of 5 and at high incident fluences the thermal coupling was roughly a factor of 2 higher than at atmospheric pressure.