Tuesday, November 9, 2004
Glass & Optical Materials Division Fall 2004 Meeting (Cocoa Beach, FL)
We investigated the morphology of femtosecond irradiated borosilicate glass with respected to two variables: the number of shots and the laser repetition rate. For the laser repetition rate we have covered the range from 250 kHz to 25 MHz. We identify two distinct regimes of femtosecond processing in the kHz to MHz range. As the time interval between pulses is reduced, we observe a transition from a repetitive modification process (identical to what is frequently called multiple shot damage) to a cumulative thermal mechanism. In the repetitive regime, each pulse acts independently and the energy deposited diffuses out of the focal volume before the next pulse arrives. In the cumulative thermal regime, the heat deposited is additive and leads to structures of significantly different morphology whose size increases dramatically with the decrease of the time interval between pulses.