  In the non-linear optical process of type-II spontaneous parametric
down-conversion, we present on an experiment showing that the two-photon
detection amplitude of the down-converted beams does not generally reproduce
the transverse profile of the pump beam that carries non-zero orbital angular
momentum. We explain this observation by that orbital angular momentum is not
conserved in the type-II non-linear process due to the broken rotational
symmetry of the Hamiltonian.
