Machining of transparent materials using an IR and UV nanosecond pulsed laser

Channels are traditionally machined in materials by drilling from the front side into the bulk. The processing rate can be increased by two orders of magnitude for transparent materials by growing the channel from the rear si de. The process is demonstrated using nanosecond laser pulses to drill mill imeter-sized channels through thick silica windows. Absorbing defects are i ntroduced onto the rear surface to initiate the coupling of energy into the material. Laser drilling then takes place when the fluence exceeds a thres hold. The drilling late increases linearly with fluence above this threshol d. While UV light drills about four times faster than TR light, the pulse l ength (in the nanosecond regime) and the pulse repetition rate (in the 0. 1 -10 Hz range) do not greatly influence the drilling rate per pulse. Drilling rates in excess of 100 mum per pulse are achieved by taking advant age of the propagation characteristics of the plasma created at the drillin g front. The plasma during rearside drilling generates a laser-supported de tonation wave into the bulk material. The geometry also seems to increase t he efficiency of the laser-induced plasma combustion and shock wave during the pulse by confining it in front of the channel tip.