Enhanced Two-Photon Absorption in a Hollow-Core Photonic Bandgap Fiber

TL;DR

This paper demonstrates significant enhancement of two-photon absorption in Rubidium atoms using a hollow-core photonic bandgap fiber, achieving high absorption with low power and confirming the role of transit time effects.

Contribution

It introduces a method to greatly enhance two-photon absorption in atomic gases within a hollow-core fiber, combining experimental results with theoretical insights.

Findings

Achieved 1% TPA with only 1 mW pump power in the fiber

Confirmed the role of transit time effects in TPA enhancement

Validated results through blue fluorescence measurement

Abstract

We show that two-photon absorption (TPA) in Rubidium atoms can be greatly enhanced by the use of a hollow-core photonic bandgap fiber. We investigate off-resonant, degenerate Doppler-free TPA on the 5S1/2 - 5D5/2 transition and observe 1% absorption of a pump beam with a total power of only 1 mW in the fiber. These results are verified by measuring the amount of emitted blue fluorescence and are consistent with the theoretical predictions which indicate that transit time effects play an important role in determining the two-photon absorption cross-section in a confined geometry.