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Modulation spectroscopy of coherent population trapping resonance and light shifts
We develop a theory of modulation response of the coherent population trapping (CPT)
resonance. We consider the simplest three-level atom, but take into account the polychromatic
spectrum of the pumping and probing light produced by pure FM modulation of single frequency
field. The analysis based on the density matrix equations rigorously includes the most important
for applications range of modulation parameters where modulation frequency and deviation are
comparable with or greater than the CPT linewidth, so the response of the atomic medium is not
adiabatic. Some theoretical results, in particular the possibility of using a quadrature response to
modulation to suppress light shift, are compared with the experiment carried out with a diode
laser (VCSEL) and 87Rb atoms.