Incubation studies and the threshold for surface damage and cavity formation in the processing of polycarbonate by Nd:YAG laser

Abstract

Polycarbonate (PC) is highly resistant to laser ablation at 532 nm. For efficient laser ablation of PC at this wavelength, it is required to use absorbing dopants or apply high fluences. This paper reports an experimental study on laser ablation of polycarbonate with a 2nd harmonic of a Q-switched Nd:YAG laser having 6 ns pulse duration at low fluence. The change in surface morphology of laser irradiated polycarbonate surface has been studied as a function of laser fluence per pulse as well as number of laser pulses. At low fluence and fewer number of laser shots, the bubbling of the laser exposed region was observed whereas at larger fluence and repeated exposer of laser for longer duration, a clear formation of the cavity was observed indicating the surface damage. Effects of variation in input laser fluence and number of pulses on ablation depth, width and ablation rate have been studied. Based on the surface morphology of the laser irradiated zone, damage threshold for polycarbonate material was found to be ∼7.35 J/cm2 per pulse with single shot and 4.41 J/cm2 with 15 number of repeated shots of laser, while 29.4 J/cm2 was noted as the ablation threshold. These results can be applied in practice to assess the parameters for laser fabrication of precise micro-cavity and channels on polycarbonate.