Analytical Expression for Continuum-continuum Transition Amplitude of Hydrogen-like Atoms with Angular-momentum Dependence

TL;DR

This paper derives an analytical expression for continuum-continuum transition amplitudes in hydrogen-like atoms, improving accuracy for low-energy and high angular-momentum states, aiding attosecond chronoscopy simulations.

Contribution

It introduces a new analytical formula based on Appell's F1 and hypergeometric functions that overcomes previous limitations in describing continuum transitions.

Findings

The formula agrees well with numerical simulations across various states.

It provides an improved description of low-kinetic-energy behavior.

The approach enhances the accuracy of attosecond chronoscopy modeling.

Abstract

Attosecond chronoscopy typically utilises interfering two-photon transitions to access the phase information. Simulating these two-photon transitions is challenging due to the continuum-continuum transition term. The hydrogenic approximation within second-order perturbation theory has been widely used due to the existence of analytical expressions of the wave functions. So far, only (partially) asymptotic results have been derived, which fail to correctly describe the low-kinetic-energy behaviour, especially for high angular-momentum states. Here, we report an analytical expression that overcome these limitations. They are based on the Appell's F1 function and use the confluent hypergeometric function of the second kind as the intermediate states. We show that the derived formula quantitatively agrees with the numerical simulations using the time-dependent Schr{\"o}dinger equation for various angular-momentum states, which improves the accuracy compared to the other analytical approaches that were previously reported. Furthermore, we give an angular-momentum-dependent asymptotic form of the outgoing wavefunction and their continuum-continuum dipole transition amplitudes.