Emission of photon pairs at discontinuities of nonlinearity in spontaneous parametric down-conversion

TL;DR

This paper explores how photon pairs are emitted at the boundaries of nonlinear materials during spontaneous parametric down-conversion, introducing a surface contribution to the process that complements the volume emission.

Contribution

It introduces the concept of surface spontaneous parametric down-conversion and describes how surface and volume contributions can be comparable in layered structures.

Findings

Surface photon pairs are emitted at nonlinearity discontinuities.

Surface and volume contributions can be of similar magnitude.

Spectral properties of surface photon pairs resemble those from volume emission.

Abstract

In order to fulfil the continuity requirements for electric- and magnetic-field amplitudes at discontinuities of chi2 nonlinearity additional photon pairs have to be emitted in the area of discontinuity. Generalized two-photon spectral amplitudes can be used to describe properties of photon pairs generated in this process that we call surface spontaneous parametric down-conversion. The spectral structure of such photon pairs is similar to that derived for photon pairs generated in the volume. Surface and volume contributions to spontaneous down-conversion can be comparable as an example of nonlinear layered structures shows.