# Photoelectron holographic interferometry to probe the longitudinal momentum offset at the tunnel exit

## TL;DR

This paper introduces a photoelectron holographic interferometry method using orthogonally polarized two-color laser pulses to accurately measure the initial longitudinal momentum of electrons at the tunnel exit, revealing nonzero momentum and non-quasi-static tunneling dynamics.

## Contribution

The study presents a novel interferometric scheme that directly measures the electron momentum offset at the tunnel exit, advancing understanding of strong-field tunneling processes.

## Key findings

- Confirmed the existence of nonzero initial longitudinal momentum at the tunnel exit.
- Demonstrated high-precision reconstruction of the momentum offset.
- Provided new insights into the non-quasi-static nature of tunneling.

## Abstract

Laser-induced electron tunneling underlies numerous emerging spectroscopic techniques to probe attosecond electron dynamics in atoms and molecules. The improvement of those techniques requires an accurate knowledge of the exit momentum for the tunneling wave packet. Here we demonstrate a photoelectron interferometric scheme to probe the electron momentum longitudinal to the tunnel direction at the tunnel exit by measuring the photoelectron holographic pattern in an orthogonally polarized two-color laser pulse. In this scheme, we use a perturbative 400-nm laser field to modulate the photoelectron holographic fringes generated by a strong 800-nm pulse. The fringe shift offers a direct experimental access to the intermediate canonical momentum of the rescattering electron, allowing us to reconstruct the momentum offset at the tunnel exit with high accuracy. Our result unambiguously proves the existence of nonzero initial longitudinal momentum at the tunnel exit and provides fundamental insights into the non-quasi-static nature of the strong-field tunneling.