Photoconductivity and excited state absorption in Cr4+:Yttrium aluminum garnet

Photoconductivity measurements were conducted on Ca2+ charge compensated Cr4+: Yttrium aluminum garnet crystals in an attempt to validate a theoretical model for saturable absorption with excited state absorption that requires transitions to the conduction band. Photocurrent was induced by absorption of 1.06 mu m laser light, accompanied by a thermally induced current of smaller magnitude. Increased photocurrent, larger by three orders of magnitude, was observed in one of the four samples suggesting the crystal exhibits increased excited state absorption. Passive Q-switch tests were performed using the four samples, with results supporting a direct correlation between photoconductivity measurements and excited state absorption. (C) 2000 American Institute of Physics. [S0021-8979(00)04317-6].