# Ground-state properties of Ca$_2$ from narrow line two-color photoassociation

## TL;DR

This study measures weakly bound vibrational levels of Ca$_2$ using two-color photoassociation, deriving precise molecular potentials, scattering lengths, and Rabi frequencies, advancing understanding of calcium dimers' ground state properties.

## Contribution

The paper provides new experimental data on Ca$_2$ vibrational levels and derives accurate long-range dispersion coefficients and scattering lengths, enhancing molecular potential models.

## Key findings

- Measured four weakly bound vibrational levels of Ca$_2$
- Derived dispersion coefficients C6, C8, C10 and scattering length 308.5(50) a0
- Determined molecular Rabi frequency consistent with theoretical models

## Abstract

By two-color photoassociation of $^{40}$Ca four weakly bound vibrational levels in the Ca$_2$ \Xpot ground state potential were measured, using highly spin-forbidden transitions to intermediate states of the coupled system $^3\Pi_{u}$ and $^3\Sigma^+ _{u}$ near the ${^3P_1}$+${^1S_0}$ asymptote. From the observed binding energies, including the least bound state, the long range dispersion coefficients $\mathrm{C}_6, \mathrm{C}_8,\mathrm{C}_{10}$ and a precise value for the s-wave scattering length of 308.5(50)~$a_0$ were derived. From mass scaling we also calculated the corresponding scattering length for other natural isotopes. From the Autler-Townes splitting of the spectra, the molecular Rabi frequency has been determined as function of the laser intensity for one bound-bound transition. The observed value for the Rabi-frequency is in good agreement with calculated transition moments based on the derived potentials, assuming a dipole moment being independent of internuclear separation for the atomic pair model.