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 side. The process is demonstrated using nanosecond laser pulses to drill millimeter-sized channels through thick silica windows. Absorbing defects are introduced onto the rear surface to initiate the coupling of energy into the material. Laser drilling then takes place when the fluence exceeds a threshold. The drilling rate increases linearly with fluence above this threshold. While UV light drills about four times faster than IR light, the pulse length (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 μm per pulse are achieved by taking advantage of the propagation characteristics of the plasma created at the drilling front. The plasma during rear-side drilling generates a laser-supported detonation wave into the bulk material. The geometry also seems to increase the efficiency of the laser-induced plasma combustion and shock wave during the pulse by confining it in front of the channel tip. Received: 1 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000