# Rydberg state ionization dynamics and tunnel ionization rates in strong electric fields

## TL;DR

This study measures tunnel ionization rates of helium Rydberg states near the classical ionization threshold using high-resolution laser techniques, comparing results with theoretical models to evaluate their accuracy.

## Contribution

It provides experimental data on ionization rates for specific Rydberg states and tests the accuracy of semi-empirical calculation methods.

## Key findings

- Measured ionization rates range from 10^5 to 10^7 s^-1.
- Measured rates are about five times larger than semi-empirical predictions.
- Comparison with theoretical models helps assess calculation accuracy.

## Abstract

Tunnel ionization rates of triplet Rydberg states in helium with principal quantum numbers close to 37 have been measured in electric fields at the classical ionization threshold of $\sim197$ V/cm. The measurements were performed in the time domain by combining high-resolution continuous-wave laser photoexcitation and pulsed electric field ionization. The observed tunnel ionization rates range from $10^5$ s$^{-1}$ to $10^7$ s$^{-1}$ and have, together with the measured atomic energy-level structure in the corresponding electric fields, been compared to the results of calculations of the eigenvalues of the Hamiltonian matrix describing the atoms in the presence of the fields to which complex absorbing potentials have been introduced. The comparison of the measured tunnel ionization rates with the results of these, and additional calculations for hydrogen-like Rydberg states performed using semi-empirical methods, have allowed the accuracy of these methods of calculation to be tested. For the particular eigenstates studied the measured ionization rates are $\sim~5$ times larger than those obtained from semi-empirical expressions.