We demonstrate a phase-shifting, point diffraction interferometer that achieves high accuracy and is capable of measuring a single pulse of light. The measurement system utilizes a polarizing point diffraction plate to generate a synthetic reference beam that is orthogonally polarized to the transmitted test beam. The plate has very high polarization contrast, works over an extremely broad angular and spectral range, and is only 100 nanometers thick. The unique features of the polarizing element make the system amenable to measuring strongly convergent light from high numerical aperture optics without the need to use a point reference source to calibrate the system. Results of measuring optics with numerical apertures as high as NA 0.8 are presented.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.