Amplitude-modulated optical double resonance
van K.A.H. Leeuwen, Michael Francis
We have investigated the interaction between
bichromatic optical fields and atomic transitions. We have
considered both the interaction of a saturating bichromatic field
in the form of a 100% amplitude-modulated field resonantly
interacting with a single atomic transition as well as the
interaction of a pair of 100% amplitude-modulated fields with two
coupled atomic transitions. In our studies of
a single atomic transition resonantly excited by a 100%
amplitude-modulated field we have used a fully
quantum-electrodynamical analysis to model the Autler-Townes effect
induced by a bichromatic optical field. We find that the effect
induced by a bichromatic field is markedly different from the
effect produced by a monochromatic exciting field. We have derived
analytic expressions for the bichromatic Autler-Townes absorption
spectrum. The absorption spectrum consists of equally spaced lines
spaced by the modulation frequency. The linewidths of neighboring
lines alternate as functions of the field strength. Experimentally,
we observed this spectrum for both resonant and detuned 100%
amplitude-modulated driving fields by monitoring the absorption of
a weak monochromatic field as it was tuned about the resonance
frequency of the 3²P₃/₂(F = 3,
mF = 3) ↔ 4²D₅/₂(F =
4, mF = 4) transition while driving the
3²S₁/₂(F = 2, mF = 2)
↔ 3²P₃/₂(F = 3, mF =
3) transition with a saturating 100% amplitude-modulated field. We
found excellent agreement between our predicted and measured
spectra. We then investigated the resonant
interaction between a pair of 100% amplitude-modulated fields and
two atomic transitions sharing a common atomic level. We considered
both a three-level atomic cascade system and a three-level atomic
lambda system. We examined the effect that the relative phase
between the two modulations has on the rate at which the modulated
fields are absorbed. We find that the saturated time-averaged field
absorption exhibits parametric resonances in both the cascade and
lambda systems. The time-averaged absorption is strongly dependent
upon the relative phase of modulation between the two fields and
for certain phase differences the time-averaged absorption can be
enhanced over the maximum saturated absorption experienced by cw
fields of the same time-averaged intensities. We also find that the
stationary atomic response exhibits periodic oscillations and for
the cascade system periodic two-photon inversions of up to 40% can
be achieved. We further find dark absorption resonances as a
function of phase in the lambda system. We analyze the results from
the point of view of semi-classical adiabatic dressed
states.
•Jan 1, 1998•0 citations