The Autler‐Townes effect in hydrogen at low pressure

The Autler‐Townes effect (also known as ac, optical or dynamical Stark splitting) on the Balmer‐α transition of hydrogen in 0.5–5 torr of helium is investigated. In the double optical resonance scheme, H(3p) is excited by absorption of two 243‐nm photons and a 656‐nm photon via the 2s resonant intermediate level. Calculated results show that in a Doppler‐free or a ‘‘Doppler‐reduced’’ beam configuration, the required intensity of the 656 nm laser (0.2 cm−1bandwidth) for observing the Autler‐Townes doublet has to be greater than 2×104 W/cm2 and 2×105 W/cm2 for a 243‐nm laser bandwidth of 0.1 cm−1 and 0.5 cm−1, respectively.