Photochromic point-diffraction inteferometer

We demonstrate a versatile and fully adaptable point diffraction interferometer (PDI) for optical testing which is based on a thin photochromic film. Pinholes are optically written in the photochromic layer, and sizes are easily customized to test optics with a wide range of focal ratios. The transparency of the layer can be tuned to optimize the contrast between the pinhole and the surrounding area and maximize the fringe visibility. Accuracy and repeatability of the photochromic PDI are determined;moreover the results are compared with those obtained with a standard Fizeau interferometer.