Abstract: A multi-beam laser Doppler vibrometer simultaneously measures velocity, displacement, and vibration history of multiple locations on an object. A beam of coherent light is split into an object beam and a reference beam. The object beam is divided into a plurality of object beams to simultaneously illuminate multiple locations on the object under inspection. The reference beam is frequency shifted and split into a corresponding plurality of frequency-shifted reference beams. A portion of each object beam is reflected by the object as a modulated object beam. The plurality of modulated object beams are collected and respectively mixed with the plurality of frequency-shifted reference beams to provide a plurality of beam pairs. Each beam pair may be focused onto a photodetector or an optical fiber connected to a photodetector.

Abstract: A method and apparatus for remotely measuring such physical properties as surface temperature and strain on or near the surface of an object such as an aerodynamic model utilizes a sensor comprising a holographic diffraction grating in a thin film, formed on or affixed to the surface of the test object, thereby forming an "optically smart surface." The sensor is remotely illuminated by one or more optical address beams, which are preferably coherent laser beams. Optical beams diffracted from the surface of the sensor produce interference patterns in a remote photodetection apparatus which permits measurement in changes in grating spatial frequency caused by temperature changes or mechanical deformations of the object surface, or Doppler measurement of particle velocity in a sample volume produced by intersecting beams diffracted from the sensor hologram.