  The influence of an ac current of arbitrary amplitude and frequency on the
mixed-state dc-voltage-ac-drive ratchet response of a superconducting film with
a dc current-tilted uniaxial cosine pinning potential at finite temperature is
theoretically investigated. The results are obtained in the single-vortex
approximation, i.e., for non-interacting vortices, within the frame of an exact
solution of the appropriate Langevin equation in terms of a matrix continued
fraction. Formulas for the dc voltage ratchet response and absorbed power in ac
response are discussed as functions of ac current amplitude and frequency as
well as dc current induced tilt in a wide range of corresponding dimensionless
parameters. Special attention is paid to the physical interpretation of the
obtained results in adiabatic and high-frequency ratchet responses taking into
account both running and localized states of the (ac+dc)-driven vortex motion
in a washboard pinning potential. Our theoretical results are discussed in
comparison with recent experimental work on the high-frequency ratchet response
in nanostructured superconducting films [B. B. Jin et al., Phys. Rev. B 81
(2010) 174505].
