Aspects of Signal Processing in Laser Vibrometry and their Embedded-Realisation on FPGA with NI-LabVIEW

The most common approach in today´s interferometric laser vibrometry is the so called heterodyne technique. This about 20 year-old method works with two optical beams with two different optical frequencies that are lead over separate ways and, after one of them has interacted with the vibrating target, are superimposed on optical detectors to produce interference signals [1] However, this concept requires expensive optical components such as a Bragg Cell or a Zeeman-Laser. In order to reduce the manufacturing cost of an interferometic laser vibrometer we persecute a strategy which reduces the optical complexity for the prize of higher signal processing demand. Based on the fact that today highly integrated signal processing hardware such as DSPs (Digital Signal Processors) FPGAs or ASICs solutions are much less expensive than in the past, this so called HWSHD (Homodyne With Synthetic Heterodyne Demodulation) strategy is therefore competitive to the classical usage of expensive optical components in the heterodyne concept. This paper will, after a brief introduction into the homodyne vibrometer concept, describe the idea and realisation aspects of the signal processing algorithm by usage of NI-LabVIEWs FPGA Module.