We discuss the schlieren imaging of quasi-sinusoidal phase objects. We demonstrate that,
when the zero-order (Fourier) spatial component of the input image is not blocked by the schlieren-knife at the Fourier plane, the intensity distribution on the reconstructed image is a linear function of the phase amplitude. In contrast, if the zero order is completely blocked
(i.e., dark Schlieren processing), the intensity distribution on the output image becomes essentially a quadratic function of the phase, and thus a direct phase retrieval is not possible.
We discuss the possibility of contrast enhancement and present validation experiments.
© 2007 Optical Society of America
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