<title>Progress in the development of the laser Doppler accelerometer</title>

Abstract

This paper outlines the principles and early development of an interferometric technique for remote measurements of vibration acceleration--laser doppler accelerometry (LDAc). The LDAc principle is not only suited to use of an inexpensive laser source but it also simplifies use for the inexpert user by removal of the requirement to match optical paths to maintain coherence. One of the most important advantages of LDAc over existing technology will be its ability to measure extremely high vibration accelerations and shocks, effectively without limit. Early development has shown how back reflections within the optical geometry are responsible for creating unwanted, velocity-dependent optical beats on the photodetector as well as the unsuitability of coherence and polarization to isolate the required acceleration-dependent beat. Novel use of a frequency shifting device, whose primary purpose is for direction discrimination, was successful in isolating the acceleration-dependent beat from the velocity-dependent beats but a problem remained in the rate at which the two beats broadened during target motion. In a further development, based again on the location of the frequency- shifting device, it was possible to 'select' a back reflection to produce a beat that was NOT modulated in the presence of target motion. The acceleration-dependent beat could then be demodulated and preliminary result are given to demonstrate this outcome.