Abstract: A method for determining a range dimension of an object utilizing multiple wavelength interferometry to form an image of the object includes developing a discernible two-dimensional image from an interference pattern at selected points for each of a number of wavelengths, collecting complex values from the interference pattern and developing a phase value from the complex value, and determining a phase correction vector based on a difference between measured phase values and an ideal phase value associated with one or more reference points. The phase correction vector is used to correct each of the selected points. A one-dimensional Fourier transform is performed on the corrected values to yield a range profile for each selected point. A peak value is then determined from the range profile to determine the range dimension. The peak value may be determined based on a simple maximum, oversampling in selected areas prior to performing the Fourier transform, or using curve-fitting techniques.

Abstract: A system for interferometric inspection of an object includes a number of improvements to reduce spurious reflections and provide precision measurement of large objects. A neutral density filter of absorptive glass is used as an attenuator to reduce undesirable reflections which may otherwise result in detector saturation. A wedge-shaped beam splitter having at least one anti-reflective surface is also utilized to reduce unwanted reflections. The system uses multiple wavelength interferometry to provide range information for an object. Additional improvements in precision may be provided by using a wavelength calibration device such as an etalon, a wavemeter, or a reference cell having relatively narrow transmission peaks, to improve the accuracy in determining the laser wavelengths. The wavelength information may be used to more precisely determine range values for the object.

Abstract: A method for determining a range dimension of an object utilizing multiple wavelength interferometry to form an image of the object includes developing a discernible two-dimensional image from an interference pattern at selected points for each of a number of wavelengths, collecting complex values from the interference pattern and developing a phase value from the complex value, and determining a phase correction vector based on a difference between measured phase values and an ideal phase value associated with one or more reference points. The phase correction vector is used to correct each of the selected points. A one-dimensional Fourier transform is performed on the corrected values to yield a range profile for each selected point. A peak value is then determined from the range profile to determine the range dimension. The peak value may be determined based on a simple maximum, oversampling in selected areas prior to performing the Fourier transform, or using curve-fitting techniques.