We present a theoretical and experimental study of spin precession in the
presence of both a static and an orthogonal oscillating magnetic field, which
is nonresonant, not harmonically related to the Larmor precession, and of
arbitrary strength. Due to the intrinsic nonlinearity of the system, previous
models that account only for the simple sinusoidal case cannot be applied. We
suggest an alternative approach and develop a model that closely agrees with
experimental data produced by an optical-pumping atomic magnetometer. We
demonstrate that an appropriately designed nonharmonic field makes it possible
to extract a linear response to a weak dc transverse field, despite the scalar
nature of the magnetometer, which normally causes a much weaker, second-order
response.Comment: Published version has some minor changes; 22 pages and 8 picture
