Experimental observations and analysis of CO2 laser-induced microcracking of glass

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Abstract
Transversely excited atmospheric pressure CO2 and modulated continuous-wave CO2 laser marking of soda-lime and borosilicate glasses has been investigated as a function of laser fluence and pulse duration. Marks are formed by a combination of surface crazing and material removal, the latter occurring predominantly through particles that are fractured from the surface. Various possible fracture mechanisms are analyzed and residual surface stress following rapid laser heating is identified as the most likely cause of microcracking. Scanning electron microscope studies show that relatively large fragments are produced, with a characteristic thickness that is dependent on the laser pulse duration, but that they predominantly remain locked in the surface. Gas phase products evolved during the interaction have also been subject to evaluation using spectroscopy of the luminous plume and fast photography techniques.