Experimental thermal coupling of laser beams

Energy in a laser beam can be transferred to a solid and increase its thermal energy. In a series of experiments, this thermal coupling has been investigated for pulsed CO2 laser beams. Target material, air pressure, focal spot size, and laser pulse separation time were varied. A feature often seen is an enhancement of the thermal coupling process above a fluence or intensity threshold. A method for the determination of the spatial profile of the heat absorbed by the target using a single on-axis thermocouple is presented. For the focal spot size and other conditions in these experiments, this technique shows a heating profile with a width much larger than the focal spot width.