Autler--Townes doublet in novel sub-Doppler spectra with caesium vapour cell

With a coupling laser locked to caesium 6S_1 / 2 F_\rm g=4--6P_3 / 2 F_\rm e=5 cycling transition and a co-propagating probe laser scanned across 6S_1 / 2 F_\rm g=4--6P_3 / 2 F_\rm e=3, 4 and 5 transitions, a novel scheme for sub-Doppler spectra in Doppler-broadened V-type three-level system is demonstrated by detecting the transmission of the coupling laser through a caesium vapour cell. The Autler--Townes doublet in the sub-Doppler spectra of the coupling laser is clearly observed. The effects of coupling laser intensity on the splitting and linewidth of the Autler--Townes doublet are experimentally investigated and the results agree well with theoretical predictions. Taking the multiple hyperfine levels of caesium atom into account, a brief analysis is presented.