Simple technique for measurements of pulsed Gaussian-beam spot sizes

A simple technique for in situ measurements of pulsed Gaussian-beam spot sizes is reported. This technique is particularly useful for measurements on highly focused beam spots. It can also be used for absolute calibration of the threshold-energy fluences for pulsed-laser-induced effects. The thresholds for several effects in picosecond-laser-induced phase transformation on silicon-crystal surfaces are calibrated with this technique.