Patent ID: 6992778

Claim:
A method for providing a signal usable to determine an offset correction for an offset component of an interferometry measurement signal provided by a detector channel in an interferometer, the interferometer comprising a reference beam path, an object beam path, at least one respective detector channel that comprises a respective detector, and an illumination source operable to provide varying-wavelength illumination, the method comprising: operating the respective detector of at least one detector channel to provide a respective signal integration period; operating the illumination source to provide a varying-wavelength illumination for the interferometer such that the varying-wavelength illumination varies over a wavelength range to provide a plurality of wavelengths distributed over the wavelength range during at least a portion of the respective signal integration period; inputting a respective interference light optical signal into the respective detector during at least a portion of the respective signal integration period, the respective interference light arising from the varying-wavelength illumination for the interferometer; and integrating a signal arising in the detector in response to the respective interference light optical signal during the respective signal integration period to provide a respective integrated signal, wherein: the plurality of wavelengths distributed over a wavelength range correspond to a plurality of optical phases of the respective interference light optical signal during at least a portion of the respective signal integration period, the plurality of optical phases distributed over an optical phase shift range corresponding to the wavelength range; the wavelength range corresponds to an optical phase shift range of at least 360 degrees; and the respective integrated signal is usable to determine an offset correction for an offset component of at least one interferometry measurement signal provided by at least that respective detector channel of the interferometer.