Control of the shape of the spatial mode function of photons generated in noncollinear spontaneous parametric down-conversion

Abstract

We show experimentally how the spatial shape of the pump beam controls the ellipticity of the spatial mode function in noncollinear spontaneous parametric down-conversion. The degree of ellipticity depends on the pump beam width, especially for highly focused beams. We introduce an effective length, the so-called noncollinear length, that determines the importance of the ellipticity of the spatial mode function. We also discuss the ellipticity induced by the spectrum of the pump beam.