Advanced Scanning Laser-Doppler Vibrometer with Computer Generated Holograms

“In this paper we present a novel technique for steering the beam of a scanning laser-Doppler vibrometer (LDV) using a Spatial Light Modulator (SLM). Computer Generated Holograms (CGH) are employed to obtain the phase maps displayed by the SLM. Due to this approach, spurious diffraction orders are generated. We present concepts to suppress these diffraction orders so as to realize a scanning vibrometer. We discuss the properties and limitations of this solution. Different SLMs have been evalutated and a compact scanning vibrometer based on a Holoeye Pluto SLM has been realized. First measurement results are presented. In addition, we demonstrate simulations on the reduction of speckle related signal dropouts. Drop-Outs can be reduced by adapting the measurement-beam wavefront with the CGH to maximize the light power collected with the vibrometer aperture. We have explored an approach to optimize the signal strength by adapting the coefficients of the Zernike polynomials of an additional wavefront shift.”