Novel adaptive single-beam laser vibrometer for vector surface-velocity measurement

摘要

Abstract: In this work, we describe a homodyne laser vibrometer that can measure all three components of surface velocity using a single probe beam and a single return beam along the line- of-sight. Our device is based on a photodetector using the photo-emf effect in GaAs. When used in a homodyne reference- beam interferometer, this detector provides an analog output signal that is proportional to the out-of-plane surface velocity. In this configuration the instrument is insensitive to slow drifts in the path length difference and can operate on speckled beams with no loss in performance. In the absence of a reference beam the same detector provides a signal proportional to the in-plane surface velocity. Both configurations can process highly speckled beams, require no setting to quadrature and are insensitive to slow phase drifts, thereby eliminating the need for path- length stabilization. We will describe the principles of operation of this instrument and report measurements to characterize its performance. !9