A comprehensive model for Doppler spectra in thermal atomic vapour

We theoretically and experimentally investigate the Doppler-broadened absorption spectrum of the D 2
-line (5 2 S 1/2 → 5 2 P 3/2 ) in thermal (room-temperature) Rb vapour over a wide range of probe
intensity, probe diameter, and vapour cell temperature to understand the effect of hyperfine pumping
and transit-relaxation on the absorption lineshape. We present a relatively simple but comprehensive
five-level rate equation model which incorporates optical pumping of the atomic population into the
other ‘dark’ ground hyperfine level (leading to absorption saturation), including contributions of
the three closely spaced (within one Doppler linewidth) hyperfine levels in the excited state 5 2 P
3/2 (allowed by the dipole transition selection rules). D 2 -line transmission spectra predicted by
our model show excellent agreement (rms error ##IMG##
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