Phase relation recovery for scanning laser Doppler vibrometry

Laser Doppler vibrometers are able to measure the velocity of a single point compared to a reference point by analyzing the Doppler shift of the laser beams. In many commercially available laser Doppler vibrometers, the laser point can be scanned to obtain an out-of-plane velocity profile of a surface. It is essential that the phase information of the velocities between points is measured as well to be able to fully reproduce the velocity profile of the surface. If this cannot be done by triggering on the actuation signal, the proposed two stage method can be used. This method measures the surface in two stages: one scan with the reference beam at a fixed point and one scan with the reference beam on a moving point. The algorithm in this article calculates the phase and reconstructs the velocity of each point. This is experimentally verified on three different micro structures. The postprocessing algorithm is not intensive in computing power.