  The lateral Casimir force, which arises between aligned sinusoidally
corrugated surfaces of a sphere and a plate, was measured for the case of a
small corrugation period beyond the applicability region of the proximity force
approximation. The increased amplitudes of the corrugations on both the sphere
and the plate allowed observation of an asymmetry of the lateral Casimir force,
i.e., deviation of its profile from a perfect sine function. The dependences of
the lateral force on the phase shift between the corrugations on both test
bodies were measured at different separations in two sets of measurements with
different amplitudes of corrugations on the sphere. The maximum magnitude of
the lateral force as a function of separation was also measured in two
successive experiments. All measurement data were compared with the theoretical
approach using the proximity force approximation and with the exact theory
based on Rayleigh expansions with no fitting parameters. In both cases real
material properties of the test bodies and nonzero temperature were taken into
account. The data were found to be in a good agreement with the exact theory
but deviate significantly from the predictions of the proximity force
approximation approach. This provides the quantitative confirmation for the
observation of diffraction-type effects that are disregarded within the PFA
approach. Possible applications of the phenomenon of the lateral Casimir force
in nanotechnology for the operation of micromachines are discussed.
