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

TL;DR

This paper demonstrates Doppler-free intermodulated fluorescence spectroscopy of helium transitions at 588 nm using a compact laser system, achieving high power and observing the first Doppler-free spectrum of spin-forbidden transitions, aiding precision QED tests.

Contribution

The study introduces a novel, compact laser system capable of Doppler-free spectroscopy of helium at 588 nm, including the first observation of spin-forbidden transition spectra.

Findings

Achieved over 1 watt of laser power at 588 nm via frequency doubling.

Observed Doppler-free spectra of helium $2^3P-3^{1}D$ transitions.

First Doppler-free spectrum of spin-forbidden $2^3P-3^1D$ transitions.

Abstract

We have demonstrated Doppler-free intermodulated fluorescence spectroscopy of helium $2^3P-3^{1,3}D$ 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 $2^3P-3^3D$ transitions were investigated. Furthermore, the Doppler-free spectrum of the spin-forbidden $2^3P-3^1D$ 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 $3^1D-3^3D$ separation.