Photochromic point-diffraction inteferometer

• A fully adaptable point diffraction interferometer (PDI) for optical testing of mirrors based on photochromic materials has been built;
• Pinhole size and semistransparency can be optically adjusted by suitable illumination of the photochromic thin film in order to match the features of the optics under measurement;
• The fringe visibility can be maximized during the interferometric measurement by a suitable laser illumination;
• The photochromic PDI is reliable and introduces small errors in the measurements comparable with a standard Fizeau interferometer.

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.