Shock-induced concentric rings in femtosecond laser ablation of glass

Both the single and multiple pulse ablation of dielectrics with high-intensity femtosecond lasers have been well studied. Additionally, the "pulse-shaping" regime, in which temporal peaks are separated by picoseconds, has also been investigated. In this paper, we show that a "prepulse configuration"-where one pulse is followed several nanoseconds later by a much stronger pulse-is qualitatively different from any of the previously investigated regimes. In particular, it leads to the recently discovered "concentric rings" feature in glass. We show that the damage pattern produced in glass is very different for two pulses separated by nanoseconds than for two pulses separated by either milliseconds or picoseconds. For nanosecond separations, the second pulse interacts with the shock wave created by the first, significantly altering the damage pattern. In addition to producing novel structures, this pump-probe technique provides a new way of studying ablation plume and shockwave dynamics. (C) 2013 AIP Publishing LLC.