Improved ionization potential of calcium using frequency-comb based Rydberg spectroscopy

TL;DR

This paper uses advanced frequency-comb spectroscopy to precisely measure calcium Rydberg energy levels, leading to a significantly improved determination of its ionization potential with high accuracy.

Contribution

It introduces a novel frequency-comb based method for measuring calcium Rydberg states and accurately determines the ionization potential, surpassing previous measurements in precision.

Findings

Ionization potential of calcium measured as 1,478,154,283.42 MHz with high precision.

Frequency-comb spectroscopy effectively eliminates Doppler broadening in Rydberg state measurements.

Achieved an 11-fold improvement over previous ionization potential determinations.

Abstract

We report new frequency-comb-based measurements of Ca Rydberg energy levels. Counter-propagating laser beams at 390 nm and 423 nm excite Ca atoms from the $4s^2~^1\mbox{S}_0$ ground state to $4sns~^1\mbox{S}_0$ Rydberg levels with $n$ ranging from 40 to 110. Near-resonant two-photon two-color excitation of atoms in a thermal beam makes it possible to eliminate the first-order Doppler shift. The resulting lineshapes are symmetric and Gaussian. We verify laser metrology and absolute accuracy by reproducing measurements of well-known transitions in Cs, close to the fundamental wavelengths of our frequency-doubled ti:sapphire lasers. From the measured transition energies we derive the ionization potential of Ca, $E_{\rm IP} = 1, 478, 154, 283.42 \pm 0.08 \mbox{(statistical)} \pm 0.07 \mbox{(systematic)}$ MHz, improving the previous best determination by a factor of 11.