Infrared point diffraction interferometer.

A point-diffraction interferometer (PDI) for use in the infrared is discussed. It is shown that the PDI is simple and easy to use and also yields fringes of constant optical path difference similar to those obtained with a Twyman–Green interferometer. The fabrication of the PDI is described, and typical results obtained using the interferometer at a wavelength of 10.6 μm are shown.