The mechanism underlying destruction of polymers by radiation from pulse-periodic CO2 laser

This study investigates the principles underlying the formation of deep (h/d 1) craters in polymethylmethacrylate specimens caused by focused radiation from a pulse periodic CO2 laser. An LGI-50 CO2 laser with pulse length of 100 micron, repetition frequency of 380 Hz and pulse energy of less than 0.05 J was employed. The parameters of the craters formed were analyzed photographically. Analysis of the cratering indicates that, in addition to waveguide processes, gas-phase processes (absorption in vapors and excitation of acoustic oscillations within the crater cavity) are significant. The acoustic currents increase the heat flux on the walls of the crater, causing local expansion; these processes restrict the possibility of achieving large crater depth-to-diameter ratios.