A Comparison of Various Coherent Optical Filtering Operations
ARNOLD ENGINEERING DEVELOPMENT CENTER ARNOLD AFB TN
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A comparison is made of different coherent optical filters with respect to their ability to locate an edge and identify phase information. These different filtering methods are bandpass filtering, the Schlieren method, the Hilbert transform method, a linear amplitude filter, and a differential filter these filters are one-dimensional. The differential filter is a combination of two filters, a linear amplitude filter and a Hilbert transform filter. A linear amplitude filter is made photographically by a programmed exposure of film to give the correct density variations. A Hilbert transform filter is a phase filter which is accomplished with a dielectric coating on glass. Bandpass filtering is accomplished by using a wire. With the use of a razor blade, the Schlieren method is achieved. The comparison of these filters indicated that bandpass filtering is superior for the location of an edge and that the Hilbert transform method is best for identifying phase information.
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