Doppler-free spectroscopy of 23Р→З3D and spin-forbidden 23P→31D transitions at 588 nm

We demonstrated the Doppler-free intermodulated fluorescence spectroscopy of the ⁴He 2³P→3¹D transitions using a one-watt compact laser system at 588 nm. The power-dependent spectra of the 2³P→3³D transitions were studied and the Doppler-free spectrum of the 2³P→3¹D transitions was first achieved.