SATURABLE ABSORBERS BASED ON IMPURITY AND DEFECT CENTERS IN CRYSTALS

Saturation of near-infrared absorption and transmission dynamics are i nvestigated in tetravalent-chromium-doped Gd3Sc2Ga3O12, Gd3Sc2Al3O12, and Mg2SiO4 crystals, as well as in reduced SrTiO3 using 20 ps 1.08 mu m laser pulses. An absorption cross section of (5 +/- 0.5) x 10(-18) c m2 in garnets and (2.3 +/- 0.3) x 10(-18) cm2 in forsterite is estimat ed for the 3A2-3T2 transition of tetrahedral Cr4+. Q-switched and ultr a-short pulses are realized in neodymium lasers using chromium-doped c rystals as the saturable absorbers. Saturation of free-carrier absorpt ion with ultrashort relaxation time is observed in SrTiO3 at 10(8)-10( 10) W/cm2 pump intensities, while at 10(10)-10(11) W/cm2 three-photon interband transitions predominate. The free-carrier absorption cross s ection is estimated to be (2.7 +/- 0.3) x 10(-18) cm2.