Quality of image conversion by a quasidegenerate four-photon interaction with tilting

The form of the spread function of a point is found for a quasidegenerate four-photon parametric interaction of the ω₁ + ω₂ – ω₁ →ω₂ type in a system with tilted pump waves. It is shown that the existence of two phase-matching directions due to a tilt of the pump waves results in doubling of the converted image of a point. When the image plane does not coincide with the optimal focusing plane, there is a critical angle of tilt of the pump waves which ensures the maximum resolution of a parametric radiation converter in the image plane. Allowance for the aperture of the pump waves alters the ratio of the maximum values of the amplitudes of the components of a doubled image of a point.