New field formulas for the Fabry - Pérot interferometer and their application to ultrasound detection

Inaccurate field formulas for light transmitted through Fabry - P?rot interferometers have been identified in the open literature. A phase lag between the first emerging ray with respect to the incident ray is generally omitted. Such an error is not important when only one type of emerging ray is investigated. However, when more than one type of ray is monitored simultaneously, such as in the application of the confocal Fabry - P?rot interferometer to the detection of ultrasound, the error leads to an inconsistency between modelling and experimental measurement. This paper presents corrected field formulas for plane and confocal interferometers, and goes on to describe ultrasound transfer functions for a confocal interferometer. These functions are shown to give good agreement with independent experimental measurements. Finally, a variety of confocal inteferometer configurations for ultrasound detection are presented, together with an outline of their essential features including their detection limits.