Observation of elliptical rings in type-I spontaneous parametric downconversion


Journal Article

© 2015 Optical Society of America. We investigate the transverse spatial profile of downconverted light produced by noncollinear, degenerate, type-I spontaneous parametric downconversion in two types of nonlinear crystals. We find that the pattern produced by one crystal, beta barium borate (BBO), produces a circular downconversion pattern while the other crystal, bismuth triborate (BiBO), produces an elliptical pattern. We show this difference is due to the angle-independent refractive index experienced by the daughter photons in BBO, while they experience an angle-dependent refractive index in BiBO. We image the transverse spatial profile of the generated light to determine the eccentricity produced by each crystal and develop a model to explain our observation. Among other things, this model predicts that there is a wavelength for which the eccentricity from BiBO is nearly zero. Finally, we discuss how the elliptical ring pattern produced in BiBO potentially affects polarization entanglement for experimental setups that collect biphotons around the entire downconversion ring. We show that the quality of polarization entanglement as measured by the overlap integral of the spectrum of the two rings can remain high (>99.4%) around the entire ring at the expense of decreased biphoton rate.

Full Text

Duke Authors

Cited Authors

  • Guilbert, HE; Wong, YP; Gauthier, DJ

Published Date

  • January 1, 2015

Published In

Volume / Issue

  • 32 / 10

Start / End Page

  • 2096 - 2103

International Standard Serial Number (ISSN)

  • 0740-3224

Digital Object Identifier (DOI)

  • 10.1364/JOSAB.32.002096

Citation Source

  • Scopus