Thin film interference with optical flats and sodium lamp.

Thin film interference with optical flats and sodium lamp. Monochromatic yellow sodium light from a sodium arc lamp shines down upon a frosted-glass diffuser-plate. The light from the plate in turn illuminates two round optical flats. The optical flats are separated by a microscopically thin layer of air. Newton's rings, or interference fringes, can be clearly seen superimposed on the optical flats.