Implementation of laser Doppler vibrometer employing holographic optical elements

We describe an implementation of a laser Doppler vibrometer system. Two main subsystems work in tandem to produce a novel and effective sensing combination. In the first subsystem, responsible for signal generation, many of the complex optical components commonly employed in more traditional vibrometry systems are replaced with holographic optical elements enabling an impressive reduction in the complexity of the system configuration and deployment. A visible light laser source is employed with obvious safety advantages over non-visible sources. Laser intensity fluctuation signals created in the sensing optics are then captured using a photodiode. In the second subsystem, responsible for the signal processing, the signal is low-pass filtered and the d.c. component of the signal is removed before it is digitised. The data is passed to a host computer where an implementation of synthetic-heterodyne demodulation is employed to detect vibration signals of at least 2 kHz. The output from this signal processing provides a measurement of the magnitude and frequency of the vibration. A simple graphical user interface controls the system's operation and displays the vibration results.