EXCITED-STATE ABSORPTION STUDIES OF CR4+ IONS IN SEVERAL GARNET HOST CRYSTALS

An experimental study of saturable absorption and excited-state absorp tion (ESA) in several inorganic saturable absorbers, Cr4+:YAG, Cr4+:GG G, and Cr4+:YSGG, is presented, We provide the theoretical background of absorption characteristics in saturable absorbers that exhibit ESA, with some new results: approximate analytical solutions are proposed for the optical transmission in the case of a slow absorber, and for v arious light intensity conditions of spatially or temporally Gaussian beams in fast and slow absorbers, Experimentally, partial bleaching of the first excited state itself could be observed in Cr4+:YAG at lambd a = 1064 nm, yielding the higher excited-state lifetime as tau = (0.5 5 +/- 0.1) ns, The regular transmission bleaching curve was measured i n Cr4+:GGG, for the first time in this material, yielding sigma(gs) = (58 +/- 5) x 10-(19) cm(2), and sigma(es) = (13 +/- 2) x 10(-19) cm(2) at lambda = 1064 nm. ESA spectra were measured for the three material s between similar to 700 and 900 nm, All three exhibit crossing betwee n saturable absorption at longer wavelengths and inverse saturable abs orption at shorter wavelengths.