  Gravitational lensing deals with general-relativistic effects in the
propagation of electromagnetic radiation. We consider wavelength-dependent
contributions in case of a (micro)lensing of an extended Gaussian source by a
point mass under standard assumptions about the incoherent emission of
different source elements. Analytical expressions for the power spectrum of a
microlensed radiation, which are effective in case of a large source, are
obtained. If the source center, the mass, and an observer are on a straight
line, the power spectrum is found in a closed form in terms of a hypergeometric
function. In the case of general locations of the lens and the source, the
result is presented in the form of a series. Approximate analytic expressions
for the power spectrum in the case of a large source and high frequencies are
obtained.
