Use of nonlinear properties of intracavity type II second harmonic generation for image processing

We discuss the use of intracavity type-II
second harmonic generation for all-optical processing of images. Injecting an image in a pump beam linearly polarized and a homogeneous field in the orthogonally polarized pump it is possible to magnify the contrast and
to recognize the contour of any part of the image whose intensity is above a tunable reference level. This can be done using ideal planar cavities where all the fields are
resonant as well as in the more realistic situation where only the fundamental fields are resonant and using cavities with spherical mirrors.