Abstract: An interferometer apparatus comprising: a short coherence length or broadband light source; a light director to direct light from the light source along a measurement path to a surface of a sample and also along a reference path to a reference surface; a wavelength disperser to cause wavelength dispersion of light along one of the measurement and the reference paths; a combiner to cause light from the sample surface and light from the reference surface to produce an interference pattern or interferogram; a detect—or to detect intensity values of the interference pattern as a function of wavelength; and a determiner to determine from the detected intensity values the wavelength at which the measurement and reference paths are balanced, wherein the wavelength disperser is at least one of: a grating wavelength disperser, a prism wavelength disperser, and an optical dispersive medium.

Abstract: Light from the first and second different wavelength light sources is combined and supplied to a director that directs zeroth order light to a reference surface and other order, generally first order diffracted light to on a location of the sample surface which is dependent upon wavelength. Light reflected by the sample and reference surfaces interfere. A characteristic of a sample surface is determined from interference light of the first wavelength. Interference light of the second wavelength is used to enable phase-locking by adjusting the path length difference by moving the reference surface or changing the refractive index of a path portion to compensate for phase variation due to environmental effects. Non-mechanical scanning is used to scan the sample surface by using a variable wavelength source and a director providing different first order diffraction angles for different wavelengths or an acousto-optical device that provides a variable pitch acoustic diffraction grating.

Abstract: Light from the first and second different wavelength light sources is combined and supplied to a director that directs zeroth order light to a reference surface and other order, generally first order diffracted light to on a location of the sample surface which is dependent upon wavelength. Light reflected by the sample and reference surfaces interfere. A characteristic of a sample surface is determined from interference light of the first wavelength. Interference light of the second wavelength is used to enable phase-locking by adjusting the path length difference by moving the reference surface or changing the refractive index of a path portion to compensate for phase variation due to environmental effects. Non-mechanical scanning is used to scan the sample surface by using a variable wavelength source and a director providing different first order diffraction angles for different wavelengths or an acousto-optical device that provides a variable pitch acoustic diffraction grating.