Variable wavelength Newton’s rings formed in transmission for measuring radius of curvature and sub-micrometric thin film thickness

In this paper, Newton’s rings interferometer was used for radius of curvature and sub-micrometric film thickness determination by varying the wavelength of the illuminating source. This was performed by using a partially reflecting spherical surface placed on a partially reflecting plane surface. The illuminating source was a halogen lamp followed by a monochromator in order to select a desired wavelength. By plotting a relation between values of wavelengths and rings’ radii for different interference orders, the radius of curvature for the used spherical surface was retrieved. In addition, the system was used to determine the thickness of a sub-micrometric thin film. This was done by depositing the film on half of the glass plane surface. The step made by the presence of the film was employed in measuring the film’s thickness. By measuring the rings’ radii in both thin film and film-free regions for different interference orders and wavelengths, we succeeded in determining the film thickness by an accurate, simple and straightforward method with a nano-metric accuracy.