The heating of polyethylene pellets with kilojoule, microsecond duration, CO2 laser pulses

Abstract

The energy absorption of 1-1.6 kJ gain-switched CO2 laser pulses focused by an approximately f/22 mirror to a spot of innermost diameter 300 mu m (FWHM) on 0.5 and 1 mm suspended cubes of polyethylene has been measured to be 75+or-13%. For plane targets the absorption was also encouragingly high, 71+or-10%. The relative insensitivity of refraction and other losses to pellet size (vis-a-vis previous short-pulse Nd laser experiments) are fully consistent with the ruby laser shadowgram and interferogram observations made towards the end of the 1.5 mu s CO2 pulse, which reveal dense cold material expanding almost randomly at velocities of approximately 0.5 mm mu s-1.