Patent ID: 7894074
Filing Date: 2011-02-22
Classification: G01H

Abstract:
1. A laser Doppler vibrometer system that employs active frequency feedback for measuring mechanical vibrations of a test object, comprising: a first optical system having a light source, the first optical system being configured to generate two beams, the first optical system having an acousto-optic modulator driven by a voltage-controlled oscillator, said acousto-optic modulator and voltage-controlled oscillator being configured to cause one of said beams to be controllably shifted in frequency relative to the other of said beams; a second optical system having a Michelson interferometer configuration, the second optical system having two arms, the two arms being configured to receive the two beams from the first optical system, wherein the first of said arms employs a reflective vibrating test object that is configured to retroreflect a first beam that travels to the reflective vibrating test object, and the other of said arms employs a static reference mirror that is configured to retroreflect a second beam that travels to the static reference mirror, and wherein the second optical system is configured to recombine the two retroreflected beams from the vibrating test mirror and the static reference mirror so as to generate an optical interference signal; a conversion device configured to receive the two beams from the second optical system, the conversion device being further configured to convert one or more optical signals into an electrical signal; a phase meter device configured to provide a phase difference between the frequency signal received from the photodetector and a reference signal, the phase meter device being further configured to output the phase difference as a voltage; a controller configured to close a feedback loop; and wherein, when the feedback loop is closed, a frequency shift imposed by the voltage-controlled oscillator cancels the Doppler shift imposed by the motion of the vibrating test object so that the phase difference between the frequency signal at the output of the photodetector and the reference signal of the phase meter is substantially zero.