A Novel Method for Measurement of the Refractive Indices of Transparent Solid Media Using Laser Interferometry

The refractive index is a number that governs how light changes its direction of propagation as it enters one material medium from another. This phenomenon is known as refraction and the angles of incidence and refraction of light, referred to the normal to the interface of the two media at the point of incidence, are related by Snell’s law. The refractive index (RI) depends on the color (or wavelength λ) of light. Tables of values of refractive indices for various media and wavelengths of light, with respect to vacuum, are readily available. The refractive index of a material can be measured by many methods, for example, by using a spectrometer in conjunction with a prism made of the experimental substance. An important class of methods of measuring RI involves the formation of interference patterns. Interferometric measurements are concerned with the study of separation between bright fringes (or dark fringes) resulting from the superposition of light waves, originating from a single source and propagating along paths of different optical lengths (refractive index multiplied by geometric path length). Researchers have exploited (nearly) monochromatic light from laser sources to enhance precision in measuring refractive index by applying interferometric techniques.