We show experimentally how noncollinear geometries in spontaneous parametric downconversion induce ellipticity of the shape of the spatial mode function. The degree of ellipticity depends on the pump beam width, especially for highly focused beams. We also discuss the ellipticity induced by the spectrum of the pump beam.
@article{arxiv.quant-ph/0508058,
title = {Shape of the spatial mode function of photons generated in noncollinear spontaneous parametric downconversion},
author = {Gabriel Molina-Terriza and Stefano Minardi and Yana Deyanova and Clara I. Osorio and Martin Hendrych and Juan P. Torres},
journal= {arXiv preprint arXiv:quant-ph/0508058},
year = {2009}
}