A two-photon wave packet (a biphoton) produced by type-II parametric downconversion is studied in a simple beam-splitting experiment for its natural shape in space–time. The measured triangular shape of a two-photon correlation function is the signature of a rectangular-shaped biphoton. Inserting a birefringent sample into the beam causes a displacement of the vertex of the notch pattern, which can be used to measure the optical delay between the ordinary and the extraordinary rays in the sample with femtosecond resolution.
© 1995 Optical Society of America
A. V. Sergienko, Y. H. Shih, and M. H. Rubin, "Experimental evaluation of a two-photon wave packet in type-II parametric downconversion," J. Opt. Soc. Am. B 12, 859-862 (1995)