Surface profiling by means of double spectral modulation

Double modulation-in frequency and intensity-of the power spectral distribution of a light beam is proposed for interferometric profilometry. The procedure is based on two facts: (1) the continuous spectrum of a light source is frequency modulated by the path difference in an interferometric device, (2) the continuous spectrum of a light source is intensity modulated by the transparency of an object placed in the exit plane of a spectroscopic device. Both procedures can be used to measure the profile of a surface with high precision. Moreover, phase shifting is automatically performed by the continuous wavelength variation along the spectrum, so that no piezoelectric transducers are necessary. The method is adaptable for the analysis of remote surfaces through optical fibers.