Phase Measurement of Resonant Two-Photon Ionization in Helium

TL;DR

This paper investigates the phase behavior of resonant two-photon ionization in helium using phase-locked high-order harmonics and interferometry, revealing how phase varies with detuning and laser intensity.

Contribution

It introduces a novel interferometric method to measure the phase of two-photon ionization processes using phase-locked harmonics.

Findings

Measured phase variation as a function of detuning

Determined intensity dependence of transition energy

Demonstrated phase measurement technique for two-photon processes

Abstract

We study resonant two-color two-photon ionization of Helium via the 1s3p 1P1 state. The first color is the 15th harmonic of a tunable titanium sapphire laser, while the second color is the fundamental laser radiation. Our method uses phase-locked high-order harmonics to determine the {\it phase} of the two-photon process by interferometry. The measurement of the two-photon ionization phase variation as a function of detuning from the resonance and intensity of the dressing field allows us to determine the intensity dependence of the transition energy.