Two-photon spectroscopy of helium 23S1-83D2,3 transitions at 544 nm with a 1.2 W compact laser system

Abstract We have demonstrated two-photon spectroscopy in a power-enhanced cavity of helium 23S1-83D2,3 transitions in a radio frequency (RF)-discharged vapor cell with a compact laser system at 544 nm. An external-cavity diode laser at 1088 nm was constructed to seed a Ytterbium-doped fiber amplifier. By employing a MgO:PPLN crystal, we have successfully doubled the laser frequency of the fiber amplifier output, generating laser power exceeding 1.2 W at 544 nm. The normalized doubling efficiency was measured to be $0.78 \%/cm\cdot{}W$.The optical power within the power-enhanced cavity was 11.8 W.Notably, the 23S1-83D2,3 transitions were observed for the first time. Subsequently, we have investigated the pressure shift and AC stark effect of the spectra.These results pave the way for precision measurement of the transition frequencies and will provide stringent test for QED atomic calculations.