Measuring thermal effects in femtosecond laser-induced breakdown of dielectrics

A quartz sample was submitted to femtosecond laser pulses with fluences up to 6xF(c), where F-c is the laser-induced breakdown fluence. A series of microthermocouples, deposited onto the surface, was used to measure heatings at the millisecond scale, at typically 50 mum from the laser impact. By using both the heat propagation equation and the Helmholtz equation to get the energy absorption profile, we estimate a minimum value of the temperature reached in the center of the crater. Even very close to F-c, this temperature is found to be greater than or similar to3000 degreesC, proving that heating effects play a major role in the breakdown of dielectrics. (C) 2002 American Institute of Physics.