Analytically controlling laser-induced electron phase in sub-cycle motion

TL;DR

This paper introduces a new analytical method to precisely control electron phase in sub-cycle motion during intense laser interactions, enabling improved manipulation of high-frequency light waves.

Contribution

The authors develop a universal analytical relation linking low-frequency electric fields to harmonic frequency shifts, validated by numerical simulations, advancing control in strong-field physics.

Findings

Validated the analytical relation with Schrödinger equation simulations.

Demonstrated potential for precise tuning of XUV waves.

Proposed a new method for sampling THz pulses.

Abstract

Precise control of the electron phase accumulated during its sub-cycle motion within intense laser fields is essential in strong-field physics, yet remains mostly indirect and complicated so far. In this Letter, we develop a novel approach to control this sub-cycle electron phase by tuning a low-frequency electric field applied on a centrosymmetric gaseous target during its interaction with a few-cycle infrared laser pulse. Our method is based on a universal analytical relation between the low-frequency electric field and its induced harmonic frequency shift, derived by the strong-field approximation. This simple relation and its universality are confirmed numerically by directly solving the time-dependent Schr\"odinger equation. Moreover, we discuss the benefits of the discovered relation in \textit{in situ} applications, including continuously and precisely tuning XUV waves and developing a new method of comprehensively sampling THz pulse.