Measurement of the refractive index of ADP and KDP crystals in the infrared range by parametric scattering of light

An argon laser was used in a study of the parametric and polariton scattering of light in ADP and KDP crystals in the range of idler wavelengths λ = 2–6.5 μ. Determination of the frequency dependence of the scattering angle made it possible to find the dispersion of the refractive index for ordinary and extraordinary waves in the range λ = 2–3 μ. It was found that ADP crystals were optically isotropic at λ = 2.22 μ and KDP crystals at λ = 2.13 μ.