We study two-photon excitation using biphotons generated via the process of spontaneous parametric down-conversion in a nonlinear crystal. We show that the focusing of these biphotons yields an excitation distribution that is essentially the same as the distribution of one-photon excitation at the pump wavelength. We also demonstrate that biphoton excitation in the image region yields a distribution whose axial width is approximately that of the crystal thickness and whose transverse width is that of the pump at the input to the crystal.
@article{arxiv.quant-ph/0110058,
title = {Biphoton focusing for two-photon excitation},
author = {Magued B. Nasr and Ayman F. Abouraddy and Mark C. Booth and Michael Kempe and Ralf Wolleschensky and Bahaa E. A. Saleh and Alexander V. Sergienko and Malvin C. Teich},
journal= {arXiv preprint arXiv:quant-ph/0110058},
year = {2009}
}