Abstract
Negative nonlinear absorption, which causes the transmission to decrease as the laser intensity increases, was observed in a 16 at. % Er:YAG crystal using a laser diode operating at 787 and 784 nm. This effect for 787 nm was strong because 787 nm was the center of an absorption peak that is related to the excited-state absorption from 4I13/2 to 2H11/2. It is suggested that these phenomena take place because the absorption cross section from 4I13/2 to 2H11/2 is larger than that from 4I15/2 to 4I9/2 using a double-absorption model.