Frequency-Domain Coherent Control of Femtosecond Two-Photon Absorption: Intermediate-Field vs. Weak-Field Regime

TL;DR

This paper analyzes femtosecond two-photon absorption in the intermediate-field regime using frequency domain methods, revealing interference effects between different transition pathways and their dependence on spectral detuning, with applications in coherent control.

Contribution

It extends perturbative analysis to the intermediate-field regime, elucidating interference effects in two-photon absorption and providing a detailed model for atomic sodium.

Findings

Interference between non-resonant and four-photon transitions affects absorption.

Detuning direction influences constructive or destructive interference.

Experimental and theoretical results agree on absorption dynamics.

Abstract

Coherent control of femtosecond two-photon absorption in the intermediate-field regime is analyzed in detail in the powerful frequency domain using an extended 4th-order perturbative description. The corresponding absorption is coherently induced by the weak-field non-resonant two-photon transitions as well as by four-photon transitions involving three absorbed photons and one emitted photons. The interferences between these two groups of transitions lead to a difference between the intermediate-field and weak-field absorption dynamics. The corresponding interference nature (constructive or destructive) strongly depends on the detuning direction of the pulse spectrum from half the two-photon transition frequency. The model system of the study is atomic sodium, for which both experimental and theoretical results are obtained. The detailed understanding obtained here serves as a basis for coherent control with rationally-shaped femtosecond pulses in a regime of sizable absorption yields.