Some optical properties of Cr 4+-doped crystals

Abstract

We summarize briefly some of our past studies, and report of preliminary recent new results concerning the optical properties of Cr 4+-doped crystals that are important for utilization as passive Q-switching devices in Nd:YAG laser systems. The host crystals involved are YAG, YSGG, GGG, LuAG and forsterite. Excited-state lifetimes of 4.0, 1.0 and 1.7 μs were measured by the Cr 4+ fluorescence decay (1.3–1.7 μm) following pulsed excitation at 1064 nm in YAG, YSGG and GGG, respectively. The ground- and excited-state absorption (ESA) cross-sections at λ=1064 nm were estimated from transmission saturation measurements. For [Cr 4+,Mg 2+]:YAG the respective results were σ gs=(3.25±0.15)×10 −18 cm 2 and σ es=(6.25±0.5)×10 −19 cm 2. In the orthorhombic forsterite, the cross-sections were polarization dependent. We got σ gs<(3.3±1)×10 −19 cm 2 for E‖ a, σ gs=(23±2)×10 −19 cm 2 and σ es=(9.0±0.7)×10 −19 cm 2 for E‖ b, and σ gs=(16±1)×10 −19 cm 2 and σ es=(5.7±0.4)×10 −19 cm 2 for E‖ c. Polarised ESA spectra were measured between 680 and 960 nm using the pulsed pump/probe technique. At 750 nm we got σ gs=(110±10)×10 −19 cm 2 and σ es=(25±3)×10 −19 cm 2 for E‖ b. Passive Q-switching performance of a flashlamp-pumped Nd:YAG laser using an intracavity [Cr 4+,Ca 2+]:GGG sample is also demonstrated.