Powder method of measuring the noncritical phase-matching frequency

Quantitative criteria are proposed for determining the noncritical phase-matching frequency from the second harmonic radiation spectrum under conditions of nonlinear conversion of the frequency of a tunable laser in powders of nonlinear crystals. The noncritical phase-matching frequencies were determined in p-nitro-p'-methylbenzalaniline and 2,4-dinitrophenol crystals. The frequency dispersion of the refractive indices of 2,4-dinitrophenol was measured.