Pulsed endoscopic digital holographic interferometry for investigation of hidden surfaces

Three systems based on digital holographic interferometry in combination with endoscopy are described. The three compact systems (using rigid, flexible endoscpoes and miniaturised head) have been developed and used for the measurement of dynamical deformations on both mechanical and biological surfaces, where measurements need to be performed at "hidden" surfaces or inside more or less closed objects. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of the CCD-camera, transferred in a frame grabber and further processed in a PC. If during the interval between the two laser pulses (usually in the range of 5-600 mus) the object undergoes a vibration, a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to quantitatively evaluate the vibration.