Mastering Interferometry: Applications and Techniques

Interferometry is a technique used to measure and analyze the interference patterns of waves. The term comes from the word interference, a phenomenon that occurs when two waves of any kind come together at the same time and place.

Interferometry has found a multitude of applications across various scientific disciplines: from space explorations to precision engineering.

The basics of Interferomtry

Interferometry makes use of interference phenomena for measurement purposes, for example investigation into the flatness of an optical surface. Even though there are many different types of interferometers, all of them basically operate on the same principle – A beam of light comes from a single coherent source and two or more flat mirrors are used to split off different light paths. These beams are then re-combined so that they interfere with each other creating an interference pattern which holds information about the differing path lengths (or more precisely the phase difference between the 2 light paths), from which analytical information surrounding the sample can be deduced.

In order to get interference a highly coherent laser source is required. The more coherent the laser beam, or the longer the coherence length, the finer the detail that can be resolved in the interferometer. This means that single longitudinal mode (ie. single frequency) lasers, with very long coherence lengths, are thus a very suitable choice of source for any interferometric application.

Interferometry with lasers

Fig.1: Interference rings for a Michelson interferometer (HeNe laser, 633nm)