Patent ID: 7511827

Claim:
An interferometer, comprising: a wavelength-variable light source configured to emit a light with a variable wavelength; a light splitting/synthesizing member operative to split the emitted light into a measurement light and a reference light and synthesize the reference light reflected from a reference surface and the measurement light reflected from a measuring object; a light splitting means operative to split the synthesized light into a plurality of split lights; a plurality of phase shifting optical members operative to provide a certain phase difference between the split lights; an imaging unit operative to image a plurality of interference fringe images formed by the phase-shifted split lights; a wavelength controller operative to control the wavelength-variable light source to vary the wavelength of the emitted light to a plurality of discrete values with a known wavelength difference between the discrete values; and an arithmetic unit operative to calculate biases, amplitudes and the phase shift of interference fringe intensities of the interference fringes formed by the plurality of split lights, based on interference fringe intensities of the imaged interference fringes, which are obtained by using part of the measuring object or by disposing a calibrating substrate instead of the measuring object, operating the wavelength controller to change the wavelength of the emitted light to a one of the plurality of discrete values for an exposure period of the imaging unit, during the exposure period varying the wavelength of the one of the plurality of discrete values over a wavelength scanning width defined by the discrete value and a wavelength shift therefrom, operating the imaging unit to image a plurality of images of interference fringes obtained by each of the plurality of split lights, the plurality of images of interference fringes obtained by each of the plurality of split lights being caused by the emitted lights with the plural discrete values, the biases, amplitudes and phase shift being calculated by solving simultaneous equations based on the interference fringes obtained by each of the plurality of split lights at the plurality of discrete wavelengths.