Spontaneous four-photon mixing in ghost imaging

A generalization of the calculation of the formation of ghost images in the course of backward four-photon mixing to the real situation of non-planar spatially limited pumping, which has a Gaussian profile of the fundamental laser mode, is developed, taking into account the specifics of the formation of phantom images. Computer images have been obtained that make it possible to estimate the spatial resolution of the systems. A relatively simple equivalent scheme for describing the process is proposed, which shows that the effect of diffraction in nonlinear systems is similar to its role in ordinary linear optics with a limited aperture. A fiber-optic version of the formation of ghost images is proposed, suitable for the study of hard-to-reach cavities and organs of the human body, which allow the introduction of a thin fiber bundle there.