Interferometry method based on changing frequency
AssigneeCoherix, Inc.
InventorMichael J. Mater
Life of this patent
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Abstract
An interferometry method using a laser of nominally fixed—but unknown and changing—frequency and phase angle, for example, attributable to laser drift. The interference pattern is periodically sampled at a frequency considerably higher than the phase shift of the object. The wavelength is reconstructed from the sampled patterns using a correlation algorithm. The phase angle is determined using an n-bucket algorithm. After all of the complex information has been determined at all of the multiple wavelengths, the surface of the object is calculated using conventional interferometry techniques. Accordingly, laser drift—typically considered a negative attribute—is used positively.
Claims18
An interferometry method comprising the steps of:
- illuminating an object at an illumination frequency to create interference patterns;
- sampling the interference patterns at a sampling frequency that is a multiple of the phase shift of the object, whereby the sampled interference patterns are collected at different phase angles;
- reconstructing the wavelength and the phase angle of the illumination frequency as a function of the sampled interference patterns;
- changing the illumination frequency and repeating the preceding steps;
- and
- creating an image of the object as a function of the collected and reconstructed complex information.
A method as defined in claim 2 wherein the sampling frequency is at least about an order of magnitude greater than the phase shift of the object.
A method as defined in claim 3 wherein the sampling frequency is about eighteen times the phase shift of the object.
An interferometry method comprising the steps of:
- creating interference patterns of an object using an illumination frequency that is changing within a known range;
- collecting the interference patterns at a sampling frequency that is a multiple of the phase shift of the object to create sampled interference patterns;
- reconstructing the wavelength and the phase angle of the illumination frequency as a function of the sampled interference patterns;
- changing the known range of the illumination frequency and repeating the foregoing steps;
- and
- creating an image of the object as a function of the collected and reconstructed complex information.
An interferometry method comprising the steps of:
- illuminating an object at a nominal but changing first frequency creating interference patterns of an object;
- repeatedly sampling the interference patterns at a second frequency at least about an order of magnitude greater than the phase shift of the object, whereby the interference patterns are sampled at least about ten times along the wavelength;
- reconstructing the wavelength and the phase angle of the first frequency as a function of the sampled interference patterns;
- selecting a different nominal frequency and repeating said illumination step, said sampling step, and said reconstructing step;
- and
- creating an image of the object as a function of the sampled and reconstructed information.
Dependencies are inferred from the claim text.