  A novel approach for measuring fast oscillations of an absolute value of
interferometer optical path difference (OPD) has been developed. The principles
of frequency-scanning interferometry are utilized for registration of the
interferometer spectral function, from which the OPD is calculated. The
proposed approach enables one to capture the absolute baseline variations at
frequencies much higher than the spectral acquisition rate. Despite the
conventional approaches, associating a single baseline indication to the
registered spectrum, in the proposed method a specially developed demodulation
procedure is applied to the spectrum. This provides an ability to capture the
baseline variations which took place during the spectrum acquisition. An
analytical model describing the limitations on the parameters of the possibly
registered baseline variations are formulated. The experimental verification of
the proposed approach and the developed model has been performed.
