This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Optical flat test with green and white light. en window resting upon an optical flat illuminated with both the green nm light from laser and white light from an incandescent bulb Image shows that the fringes are fairly straight with some small deviations indicated that the surface of the window in very close to flatness The flat