We summarize briefly some of our past studies, and report of preliminary re
cent new results concerning the optical properties of Cr4+-doped crystals t
hat are important for utilization as passive Q-switching devices in Nd:YAG
laser systems. The host crystals involved are YAG, YSGG, GGG, LuAG and fors
terite. Excited-state lifetimes of 4.0, 1.0 and 1.7 mu s were measured by t
he Cr4+ fluorescence decay (1.3-1.7 mu m) following pulsed excitation at 10
64 nm in YAG, YSGG and GGG, respectively. The ground- and excited-state abs
orption (ESA) cross-sections at lambda = 1064 nm were estimated from transm
ission 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 we
re polarization dependent. We got sigma(gs) < (3.3 +/- 1) x 10(-19) cm(2) f
or 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 para
llel 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 us
ing an intracavity [Cr4+,Ca2+]:GGG sample is also demonstrated. (C) 1999 El
sevier Science B.V. All rights reserved.