Two-step excitation and blue fluorescence under continuous-wave pumping in Nd:YLF

Abstract

Near-UV and blue fluorescence from the 4D3/2 and 4D5/2 manifolds in Nd:YLF has been observed at room temperature under cw pumping by a Rhodamine 590 dye laser. Excitation to these manifolds is attributed to two-step excitation involving excited-state absorption from the 4F3/2 metastable level. A similar phenomenon has also been observed in Nd:YAG and Nd:glass. The effective excited-state absorption cross section is measured to be (2 ± 1) × 10−20 cm2 at 587.4 nm in the π polarization, and the peak effective stimulated emission cross section is measured to be 5 × 10−20 cm2 at 411.7 nm, also in the π polarization. Estimated laser threshold at 411.7 nm for two-step pumping at 587.4 nm is 70 mW.