Heterodyning of speckle shearing interferometers by laser diode wavelength modulation

Laser diode emission wavelength modulation is demonstrated as a technique for measuring the phase and gradient of displacement amplitude of a vibrating object using continuous wave illumination in a path length imbalanced speckle shearing interferometer. The unwanted mismatch in the magnification of the two images in the shearing interferometer and sensitivity to radial shear introduced by a path length imbalance is overcome by the use of a transparent block of high refractive index in one path in the interferometer.