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It is known that spectral properties of the Fabry - Perot interferometer(FPI) depend on the spatial characteristics of the incident radiation. Thispaper proposes a general method for taking this dependence into account, basedon the decomposition of the incident field into the angular spectrum of planewaves, which are the FPI eigenfunctions. In the scalar approximation, theangular-frequency transfer function and the point-spread function (Greenfunction) of the FPI are calculated, which enables to relate the spatialcoherence functions of the incident and transmitted radiation and to derive anexpression for the output intensity I(r, k) and for the integral transmittanceP(k) depending on the wavenumber of the incident monochromatic radiation k. Inthe resulting expressions, I(r, k) is completely determined by the Fouriertransform of the input coherence function, and P(k) is determined by theangular power spectrum (APS) of the incident radiation. For beams of smalldivergence and high-quality FPIs, simplified formulas have been obtained thatallow, in the first approximation, for the dependence of the FPI parameters onthe angle of incidence and on the radiation wavelength. Analysis of theexpressions obtained makes it possible to clarify an exact meaning of thewell-known regularities in the distortions of the FPI transmission bandassociated with the incident beam deviation from the plane wave (shift to theshortwave region, broadening, reduction of the maximum transmittance and theappearance of asymmetry). As examples, calculations of the integraltransmittance for three types of APS, corresponding to Gaussian and conicalbeams, and the output intensity distribution I(r, k) for the input beam with aGaussian APS are performed. Results are consistent with other theoretical andexperimental works.

Spectral characteristics of the Fabry-Perot interferometer transmission upon illumination by an arbitrary light beam