Coherent Control of Resonant Two-Photon Transitions by Counter-Propagating Ultrashort Pulse Pairs

TL;DR

This paper demonstrates a method for coherently controlling two-photon atomic transitions using counter-propagating ultrashort laser pulses with spectral phase programming, enabling spatially selective excitation in a three-state system.

Contribution

It introduces an experimental approach combining spectral phase-flipping with spatial coherent control to isolate two-photon transitions from background signals.

Findings

Successful experimental control of two-photon transitions with phase-flipped pulses.

Enhanced spatial selectivity of excitation patterns.

Effective suppression of resonance-induced background signals.

Abstract

We describe optimized coherent control methods for two-photon transitions in atoms of a ladder-type three-state energy configuration. Our approach is based on the spatial coherent control scheme which utilizes counter-propagating ultrashort laser pulses to produce complex excitation patterns in an extended space. Since coherent control requires constructive interference of constituent transition pathways, applying it to an atomic transition with a specific energy configuration requires specially designed laser pulses. Here, we show, in an experimental demonstration, that the two-photon transition with an intermediate resonant energy state can be coherently controlled and retrieved out from the resonance-induced background, when phase-flipping of the laser spectrum near the resonant intermediate transition is used. A simple reason for this behavior is the fact that the transition amplitude function (to be added to give an overall two-photon transition) changes its sign at the intermediate resonant frequency, thus, by a proper spectral-phase programming, the excitation patterns (or the position-dependent interference of the transition given as a consequence of the spatial coherent control) are well isolated in space along the focal region of the counter-propagating pulses.