LASER-INDUCED CRACK UNDER PULSE-PERIODIC RADIATION.

It is well known that disk-like cracks are formed in the bulk of polymer glass subjected to a laser pulse of duration tau //u approximately 10** minus **3 sec and power density q exceeding the rupture threshold q approximately 10**5 W/cm**2. In this case cracks occur because of an internal micro-explosion absorbing the light with the formation of a microcrack. The regime of crack growth from a microcrack under the pulse-periodic action of a low-power focused laser beam is investigated in this paper. In this regime the growth of the crack 2 is accompanied by the occurrence of an absorption wave 1 being propagated towards the laser beam 3 along a caustic where gas particle formation occurs not on the surfaces constraining the crack but in the irradiated tip of the absorption wave. The brightness temperature, measured by a photographic method, reached 1200 degree K in the area of progress of laser pyrolysis (at the tip of the absorption wave).