US 4,913,547 A · Optically phased-locked speckle pattern interferometer

Abstract

An optically phase-locked electronic speckle pattern interferometer mixes a local oscillator beam with a beam reflected from a target surface to create a speckle pattern at each of two separate image planes. The speckle pattern includes speckles whose intensities vary as a result of time-varying Doppler shifting of the reflected beam by movement or deformation of the target surface. The local oscillator beam is phase-locked to the Doppler signature of a lock-point speckle on one image plane. The phase-locking of the local oscillator beam to Doppler information of interest enables the interferometer to coherently detect speckle in the image plane sharing frequency, amplitude, and phase characteristics with the lock-point speckle, which supports the efficient processing of images obtained from the other image plane. The processing produces a contoured image of the target surface, with demarcation between coherently and non-coherently detected speckle.

Claims27

Dependent claims

A method for phase-locked optical interferometric inspection of a surface, comprising the steps of:

producing a first beam of energy by reflection from a target surface;
producing a second beam of energy having signal characteristics, said signal characteristics including frequency and phase;
mixing said first and second beams to produce a first interference pattern at a first image plane and a second interference pattern at a second image plane;
from a portion of said second interference pattern, deriving a control signal with frequency and phase characteristics representing a modulation of said first beam;
in response to said control signal, changing a signal characteristic of said second beam in synchronism with said modulation;
and
generating successive images from said first interference pattern and combining said successive images to produce a contoured target surface image.

4 more elements

An optical, phase-locked speckle pattern interferometer, comprising:

an image processor with a display, responsive to a succession of interference image signals for generating a sequence of interference images, and for combining successive interference images for production of a contoured target surface image on said display;
an optical circuit for receiving a first beam of light by reflection from a target surface and for generating a second beam of light having signal characteristics of phase and frequency, and for mixing said first and second beams to produce respective first and second interference patterns;
a first imaging apparatus with a first imaging plane for receiving said first interference pattern at said first imaging plane to generate said succession of interference image signals, each of said interference signals corresponding to a speckle pattern image of a target surface;
a second imaging apparatus with a second imaging plane for receiving said second interference pattern at said second imaging plane to generate from said second interference pattern a control signal with frequency and phase characteristics representing speckle modulation of said first beam by said target surface;
and
an electro-optical locking circuit connected to said optical circuit and to said second imaging apparatus for changing a signal characteristic of said second beam in synchronism with said modulation, said signal characteristic changing being in response to said control signal.

3 more elements

Dependencies are inferred from the claim text.

Optically phased-locked speckle pattern interferometer

Life of this patent

Optically phased-locked speckle pattern interferometer

Life of this patent

Abstract

Claims27