Automatic measurement of in-plane translation by speckle correlation using a linear image sensor

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Abstract
A speckle correlation method for measuring the in-plane translation of a diffuse object using a linear image sensor followed by a microcomputer is studied in detail. Displacement of a speckle pattern arising in the diffraction field of the object illuminated by a narrow laser beam is detected from the peak position of the cross-correlation between the sensor outputs before and after object translation along the sensor axis. This speckle displacement is proportional to the object translation. The sensitivity of the measurement can be adjusted over a wide range by changing the radius of the wavefront curvature of the incident beam. The influences of the size of the beam and pixel number of the sensor have also been examined.