  We study polarization effects in the nonlinear interference of photons
generated via frequency non-degenerate spontaneous parametric down conversion.
Signal and idler photons generated in the visible and infrared (IR) range, are
split in different arms of a nonlinear Michelson interferometer. The
interference pattern for signal photons is detected, and it is shown to be
dependent on the polarization rotation of idler photons, introduced by a
birefringent sample. Based on this concept, we realize two new methods for
measurement of sample retardation in the IR range by using well-developed and
inexpensive components for visible light. The accuracy of the methods meets
current industry standards. The developed IR polarimetry technique is relevant
to material research, optical inspection, and quality control.
