Laser beam characteristics using dc-induced second harmonic generation.

Previous measurements of electric field induced second harmonic generation indicated that the confocal parameter for a laser beam as calculated from the second harmonic intensity profile was in disagreement with that calculated from the measured beam diameter. In this paper, we show that this discrepancy is caused by the departure of the beam from the pure TEM(00) mode. We expand a distorted beam in terms of the component modes by using the experimental beamscan and calculate the second harmonic profile using this expansion. This calculational procedure is found to be consistent with experimental observations.