The conservation of orbital angular momentum and the two-photon detection amplitude in spontaneous parametric down-conversion

Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208-3112, U.S.A.(Dated: February 1, 2008)We study the two-photon detection amplitude of the down-converted beams in spontaneous para-metric down-conversion when the physical variable of orbital angular momentum is involved, takinginto account both conservation and non-conservation of angular momentum. Agreeing with ex-perimental observations, our theoretical calculation shows that spatial structure of the two-photondetection amplitude of the down-converted beams carries important information about conservationor non-conservation of orbital angular momentum in spontaneous parametric down-conversion.