Effect of radiation trapping on fluorescence lifetime and emission cross section measurements in solid-state laser media

TLDR

Radiation trapping significantly lengthens measured fluorescence lifetimes in optically thin solid‑state laser gain media, causing up to 30 % underestimates of stimulated emission cross sections. The study demonstrates a measurement technique that greatly reduces radiation trapping in Yb:YAG, a prototypical quasi‑three‑level laser medium. The technique applies a novel measurement approach to Yb:YAG that minimizes radiation trapping effects. The radiative lifetime of the 2F5/2 manifold was measured to be 0.951 ms at 300 K—over 10 % lower than prior values—yielding a 1.03‑µm peak effective stimulated emission cross section of 2.3 × 10⁻²⁰ cm², and the method is most relevant for three‑level and quasi‑three‑level laser media.

Abstract

Radiation trapping causes significant lengthening of the measured fluorescence lifetime in optically thin solid-state laser gain media, which leads to underestimates of the stimulated emission cross section by as much as 30%. A measurement technique is demonstrated that greatly reduces radiation trapping in Yb:YAG, a prototypical quasi-three-level laser medium. The radiative lifetime of the 2F5/2 manifold was measured to be 0.951 ms at 300 K, which is more than 10% lower than any previous measurement. This more-accurate radiative lifetime gives a 1.03-μm peak effective stimulated emission cross section of 2.3 × 10−20 cm2. Our measurement technique is expected to be most relevant for three-level and quasi-three-level laser media.