Enhancement of Intermediate-Field Two-Photon Absorption by Rationally-Shaped Femtosecond Pulses

TL;DR

This paper extends frequency-domain analysis of femtosecond two-photon absorption to the intermediate-field regime, identifying shaped pulses that enhance absorption and experimentally verifying these findings for sodium, enabling improved coherent control.

Contribution

It introduces a theoretical framework for intermediate-field two-photon absorption with shaped pulses and experimentally confirms the enhancement in sodium, advancing coherent control techniques.

Findings

Broad family of shaped pulses enhances absorption

Anti-symmetric spectral phase around half transition frequency is effective

Experimental verification in sodium confirms theoretical predictions

Abstract

We extend the powerful frequency-domain analysis of femtosecond two-photon absorption to the intermediate-field regime, which involves both two- and four-photon transitions. Consequently, we find a broad family of shaped pulses that enhance the absorption over the transform-limited pulse. It includes any spectral phase that is anti-symmetric around half the transition frequency. The spectrum is asymmetric around it. The theoretical framework and results for Na are verified experimentally. This work opens the door for rational femtosecond coherent control in a regime of considerable absorption yields.