Detailed balance limits for inversion in solar-pumped lasers and allied systems

Solar-pumped lasers and optical amplifiers continue to draw research interest with advances in nanomaterials science and technology. Establishing accurate detailed balance limits for inversion in these systems is essential. In this Letter, we re-examine the threshold limits for inversion in broadband-pumped lasers, with reference to those provided by Roxlo and Yablonvitch [Opt. Lett.8, 271 (1983)OPLEDP0146-959210.1364/OL.8.000271], where they determined the minimum Stokes shift and the minimum ratio of pump band to emission band absorption constants-based on independent consideration of the emission at pump and emission frequencies. In contrast, the derivation here simultaneously accounts for emission in both the pump and emission bands, which in turn leads to a single consolidated inequality that serves to establish the revised threshold requirements for inversion. Upon applying this new unified relationship to solar-pumped devices, a large increase in the minimum required Stokes shifts for 1-sun devices, particularly at larger pump energies and smaller ratios of α/α, is found. The maximum possible efficiencies of solar-pumped devices are calculated using this new relation.