dc-Induced Optical Second-Harmonic Generation in the Inert Gases

We have measured dc-induced optical second-harmonic generation by a focused laser beam; we verify the predicted dependence on geometric and physical parameters, thus providing a novel method of probing the confocal parameter at the laser focus. In addition, we have deduced values of ${\chi }_{\mathrm{yyyy}}(-2\mathrm{}\omega ;0,\omega ,\omega )$ for the inert gases, and we find good general agreement with various other data.