Picosecond laser-induced damage morphology: Spatially resolved microscopic plasma sites

The morphology just above threshold of damage sites caused by picosecond 1.06 μm laser pulses is shown to consist of a collection of micron-sized, spatially distinct vestiges of individual plasmas. From the observed site density, the density of electrons which may initiate breakdown can be inferred. The morphology is consistent with an avalanche ionization model, but not with absorbing inclusion damage.