High-speed, sub-Nyquist interferometry

The velocity measurement limit in dynamic interferometry is v(Nyq), the velocity at which the interferogram is sampled at the Nyquist limit. We show that v(Nyq) can be exceeded by assuming continuity of the surface motion and unwrapping the velocity modulo 2v(Nyq). The technique was demonstrated in a high-speed speckle pattern interferometer with spatial phase stepping. Surface velocities of 4v(Nyq) were measured experimentally. With a reduced exposure, high-speed sub-Nyquist interferometry could be implemented up to a maximum acceleration of v(Nyq/ts), where t(s) is the detector frame period. (C)2011 Optical Society of America