Miniaturized Optical Sensor for Leak Detection in a Space Environment

A miniature optical, laser-based, interferometric leak detector is presented for application as a means to detect on-orbit gas leaks. The sensor employs a fiber-coupled modified Michelson interferometer to detect gas leaks by measuring an increase in gas density in the sensing region. Monitoring changes in the fringe pattern output by the interferometer allows for direct measurement of the gas density in the sensing region and, under the assumption of an equation of state, this can be used to obtain a pressure measurement. Measurements obtained over a pressure range from 20 mtorr to 760 torr using a prototypical interferometer on working gases of air, nitrogen, argon, and helium generally exhibit agreement with a theoretical prediction of the pressure increase required before an interference fringe completely moves Over the detector. Additional measurements performed on various gases demonstrate the range of detectable species, measuring subtorr pressure changes in the process. Time-resolved data prove the capability of this sensor to detect fast gas flow phenomena associated with transients and pressure waves.