Comparison of different approaches to the longitudinal momentum spread after tunnel ionization

TL;DR

This paper presents a new method to measure the longitudinal momentum spread after tunnel ionization in Helium, valid for all laser ellipticities, and compares semiclassical models with experimental data.

Contribution

It introduces a versatile measurement approach and highlights the importance of initial longitudinal spread in semiclassical modeling of tunnel ionization.

Findings

Semiclassical models match experimental results when initial longitudinal spread is included.

The initial longitudinal spread is approximately twice the transverse momentum spread.

The method is applicable across all ellipticities of laser pulses.

Abstract

We introduce a method to investigate the longitudinal momentum spread resulting from strong-field tunnel ionization of Helium which, unlike other methods, is valid for all ellipticities of laser pulse. Semiclassical models consisting of tunnel ionization followed by classical propagation in the combined ion and laser field reproduce the experimental results if an initial longitudinal spread at the tunnel exit is included. The values for this spread are found to be of the order of twice the transverse momentum spread.