Time-resolved studies of short pulse laser-produced plasmas in silicon dioxide near breakdown threshold

Using the technique of frequency-domain interferometry, we demonstrate a ne w way of studying: laser-induced breakdown at the surface of dielectric mat erials. A theoretical model based on electron production by multiphoton ion isation, inverse bremsstrahlung heating, and collisional ionisation is in q uantitative agreement with both the detailed time variation of tilt: dielec tric constant and the pulse width variation of the fluence threshold. From the complex reflection coefficient measured with the two probe pulse polari sations in quadrature, we deduce the time variation of the dielectric const ant of silica during breakdown.