US Government As Represented by the Secretary of the Army

James D Perea

Bradley W Libbey

A phase-resolved heterodyne shearing interferometer has been developed for high-rate, whole field observations of transient surface motion. The sensor utilizes polarization multiplexing and multiple carrier frequencies to separate each segment of a shearing Mach-Zehnder interferometer. Post-processing routines have been developed to recombine the segments by extracting the scattered object phase from Doppler shifted intermediate carrier frequencies, providing quantitative relative phase changes and information to create variable shear, phase resolved shearographic fringe patterns without temporal or spatial phase shifting.

Method for phase resolved heterodyne shearographic measurements

A multi-axis heterodyne interferometer is disclosed for observations of five degrees of dynamic freedom using a single illumination source. The sensor utilizes polarization and frequency multiplexing to simultaneously observe and separate the image and Fourier planes following scattering of coherent illumination from a dynamic surface. Multiple carrier frequencies and polarizations separate two segments of a Mach-Zehnder interferometer. Segments of this interferometer have unique optical configurations to generate the image and Fourier planes simultaneously on a focal plane array. The measured irradiance contains information pertaining to an object's in-plane translation, out-of-plane rotation, and out-of-plane displacement.

Apparatus for a dynamic multi-axis heterodyne interferometric vibrometer

Method and apparatus for phase resolved heterodyne shearographic measurements

A laboratory system has demonstrated the measurement of three degrees of vibrational freedom simultaneously using a single beam through heterodyne speckle imaging. The random interference pattern generated by the illumination of a rough surface with coherent light can be exploited to extract information about the surface motion. The optical speckle pattern is heterodyne mixed with a coherent reference. The recorded optical data is then processed to extract three dimensions of surface motion. Axial velocity is measured by demodulating the received time-varying intensity of high amplitude pixels. Tilt, a gradient of surface velocity, is calculated by measuring speckle translation following reconstruction of the speckle pattern from the mixed signal.

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Alexandria, VA, United States of America

James D Perea