Doppler-free intermodulated fluorescence spectroscopy of 4He 23P-31,3D transitions at 588 nm with a 1-W compact laser system

We have demonstrated Doppler-free intermodulated fluorescence spectroscopy of helium 2(3)P-3(1,3)D transitions in an rf-discharged sealed-off cell using a compact laser system at 588 nm. An external cavity diode laser at 1176 nm was constructed to seed a Raman fiber amplifier. Laser power of more than 1 W at 588 nm was produced by frequency doubling of the fiber amplifier output using a MgO:PPLN crystal. A doubling efficiency of 23 % was achieved. The power-dependent spectra of the 2(3)P-3(3)D transitions were investigated. Furthermore, the Doppler-free spectrum of the spin-forbidden 2(3)P-3(1)D transitions was observed for the first time. Our results are crucial toward precision test of QED atomic calculations, especially for improving the determination of the helium 3(1)D-3(3)D separation.