Doppler-free intermodulated fluorescence spectroscopy of ${}^{4}He$ $2^{3}P-3^{1,3}D$ transitions at 588 nm with a one-watt compact laser system

Abstract

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 one watt 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 towards precision test of QED atomic calculations, especially for improving the determination of the helium $3^{1}D-3^{3}D$ separation.

6 pages, 5 figures

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