The interferometer is a quick and easy way to measure the thickness of a dielectric thin film.

When an electromagnetic wave is shined on a thin film, the reflection and transmission of the wave between media creates interferences patterns.  Component wavelengths from 200 nm to 900 nm are typical.  These wavelengths are ultraviolet (10 nm to 400 nm), visible light (380 to 750 nm), and short infrared (700 nm to 300 um).

Spectrophotometry is used to calculate the intensity of the reflected light as a function of wavelength.  The Fresnel equations are used for curve fitting and the thickness of the single-layer transparent film are obtained.