The present invention provides an optical filter assembly that reduces the
phase and amplitude noise of a detection laser used to detect ultrasonic
displacements. The filtered detection laser is directed to the surface of
a remote target. Ultrasonic displacements at the surface scatter the
filtered detection laser. Collection optics then gather phase modulated
light scattered by the surface and direct the phase modulated light to an
optical processor to produce a signal representative of the ultrasonic
displacements with an improved SNR. Additional processors may determine
the structure of the remote target.