Automatic deformation analysis by a TV speckle interferometer using a laser diode

A phase-shifting TV speckle interferometer is developed by using the frequency modulation capability of a laser diode and is applied to automatic deformation measurements. Temperature modulation is used for generating the frequency shift of a laser diode. We store four speckle interferograms with relative phase differences of pi/2 in a frame grabber by monitoring a phase-shift signal, which is obtained by integrating the fringe intensity over a local window. The optimum size of the local window is examined experimentally. Then, the optimum processing conditions for reducing the speckle noise in interferograms,including an averaging window size, are found. Experimental results of the automatic deformation analysis indicate a displacement accuracy of better than lambda/30.