Optimized Phase Masks for Absorption of Ultra-Broadband Pulses by Narrowband Atomic Ensembles

TL;DR

This paper uses genetic algorithms and phase masks to optimize two-photon absorption in atomic ensembles, achieving significant enhancement factors and analyzing implications for ultra-broadband photon storage.

Contribution

It introduces a method combining genetic algorithms and phase masks to enhance two-photon absorption in atomic ensembles, with detailed analysis of various configurations and parameters.

Findings

Enhancement factor of 9.5 for sequential photons from the same pulse.

Enhancement factor of 26 for photons from different pulses.

Up to 3-fold increase in absorption at high optical depths.

Abstract

By combining genetic algorithm and a spatial light modulator we theoretically analyse how to improve a two-photon cascade absorption in atomic ensembles, inspecting the impact of various configurations and parameters in the optimized phase mask. At low atomic densities, we compare the cases of sequential transitions with the two photons coming from the same pulse or from two different pulses. For the former, we predict an enhancement by a factor of $9.5$, similar to what was previously reported in the literature [Phys. Rev. Lett. {\bf 86}, 47 (2002)]. For the later, on the other hand, we obtain an enhancement factor of $26$ times. This absorption of two photons by different pulses is of particular interest for the storage of ultra-broadband single photons by atomic ensembles, in which case the second photon would come from a control pulse. We investigate this process as a function of the atomic density, demonstrating enhancements by factors up to 3 for the two-photon absorption after propagating through large optical depths. However, for the experimental conditions considered in the previous work by Carvalho {et al.} [Phys. Rev. A {\bf 101}, 053426 (2020)], in terms of control power and optical depths, we show that this enhancement in two-photon absorption would still result in just a modest increase of the absorption of a weak probe pulse.