  In recent years diode laser sources have become widespread and reliable tools
in magneto-optical spectroscopy. In particular, laser-driven atomic
magnetometers have found a wide range of practical applications. More recently,
so-called magnetically silent variants of atomic magnetometers have been
developed. While in conventional magnetometers the magnetic resonance
transitions between atomic sublevels are phase-coherently driven by a weak
oscillating magnetic field, silent magnetometers use schemes in which either
the frequency (FM) or the amplitude (AM) of the light beam is modulated. Here
we present a theoretical model that yields algebraic expressions for the
parameters of the multiple resonances that occur when either amplitude-,
frequency- or polarization-modulated light of circular polarization is used to
drive the magnetic resonance transition in a transverse magnetic field. The
relative magnitudes of the resonances that are observed in the transmitted
light intensity at harmonic m of the Larmor frequency \omega_L (either by DC or
phase sensitive detection at harmonics q of the modulation frequency
\omega_mod) of the transmitted light are expressed in terms of the Fourier
coefficients of the modulation function. Our approach is based on an atomic
multipole moment representation that is valid for spin-oriented atomic states
with arbitrary angular momentum F in the low light power limit. We find
excellent quantitative agreement with an experimental case study using
(square-wave) amplitude-modulated (AM) light.
