Patent ID: 7173212

Claim:
A method for modifying a material surface using one or more lasers, comprising: applying a laser pulse to a desired laser beam interaction zone on said material surface for a predetermined period t 1 at a predetermined power level P 1 such that processed material melts and evaporates, producing evaporation induced recoil which displaces produced melt to a periphery of the interaction zone without substantial ejection of molten material from said laser beam interaction zone, thereby creating a keyhole in the material; applying a laser pulse to said laser beam interaction zone for a predetermined period t 2 at a different predetermined power level P 2 such that the induced evaporation recoil is insufficient to counteract surface tension pressure and a controlled collapse of said keyhole occurs while maintaining a temperature of produced melt above a melting temperature of said material; applying a laser pulse to said laser beam interaction zone for a predetermined period t 3 at a predetermined power level P 3 that is different from power levels P 1 and P 2 such that rapid evaporation of the molten material is induced, generating recoil which produces near complete ejection of the melt created during the first period t 1 , and thus forming a crater; and applying a laser pulse to said laser beam interaction zone for a predetermined period t 4 at a predetermined power level P 4 that is different from power levels P 1 , P 2 , and P 3 such that a temperature of the remaining melt which was not ejected from the interaction zone and a temperature of the solid material near a wall of said crater decreasing at a controlled rate which is below a cooling rate which would ordinarily produced microcracking of said material.