Saturation of 1047- and 1064-nm Absorption in Cr@@u4+@:YAG Crystals

To investigate the physical mechanism of the saturation process in Cr@@u4+@:YAG crystals we solved the three coupled rate equations which describe the saturable absorber. We experimentally verified this model using two lasers with nanosecond pulses and continuous-wave radiation. We used crystalline and ceramic Cr@@u4+@-doped YAG saturable absorbers with various initial transmissions. The ratio between the ground and the excited-state absorption cross section at 1064 nm was measured to be between 3.8 plusmn 0.2 and 4.7 plusmn 0.2 for crystalline and 3.6 plusmn 0.1 for ceramic Cr@@u4+@:YAG. The ratio between the above named cross sections at 1047 nm was found to be 6.2 plusmn 0.2 for both crystalline and ceramic Cr@@u4+@:YAG. With these results the ground-state and the excited-state absorption cross sections at 1047 nm were calculated to be (9.55plusmn0.01)times10@@u-19@ cm@@u2@ and (1.54plusmn0.03)times10@@u-19@ cm@@u2@, respectively.