Some optical properties of Cr4+-doped crystals

We summarize briefly some of our past studies, and report of preliminary recent new results concerning the optical properties of Cr4+-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 mu s were measured by the Cr4+ fluorescence decay (1.3-1.7 mu m) following pulsed excitation at 1064 nm in YAG, YSGG and GGG, respectively. The ground- and excited-state absorption (ESA) cross-sections at lambda = 1064 nm were estimated from transmission saturation measurements. For [Cr4+,Mg2+]:YAG the respective results were sigma(gs) = (3.25 +/- 0.15) x 10(-18) cm(2) and sigma(cs) = (6.25 +/- 0.5) x 10(-19) cm(2). In the orthorhombic forsterite, the cross-sections were polarization dependent. We got sigma(gs) < (3.3 +/- 1) x 10(-19) cm(2) for E parallel to a, sigma(gs) = (23 +/- 2) x 10(-19) cm(2) and sigma(es) = (9.0 +/- 0.7) x 10(-19) cm(2) for E parallel to b, and sigma(gs) = (16 +/- 1) x 10(-19) cm(2) and sigma(es) = (5.7 +/- 0.4) x 10(-19) cm(2) for E parallel to c. Polarised ESA spectra were measured between 680 and 960 nm using the pulsed pump/probe technique. At 750 nm we got sigma(gs) = (110 +/- 10) x 10(-19) cm(2) and sigma(es) = (25 +/- 3) x 10(-19) cm(2) for E parallel to b. Passive Q-switching performance of a flashlamp-pumped Nd:YAG laser using an intracavity [Cr4+,Ca2+]:GGG sample is also demonstrated. (C) 1999 Elsevier Science B.V. All rights reserved.