Optical nonlinearities of glass doped with PbS nanocrystals

Nonlinear absorption of glass doped with PbS nanocrystals is studied and ap plication of this composite material as a saturable absorber for mode locki ng in lasers is discussed. By using time resolved absorption pump-probe inv estigation, bleaching due to filling of discrete states caused by quantum c onfinement in the nanocrystals as well as induced absorption are revealed a nd characterized. The origin of the induced absorption is discussed. Kineti cs of the transient absorption is studied. Two components observed in the d ecay of the nonlinearities are observed and interpreted in terms of the car rier trapping. (C) 2000 American Institute of Physics. [S0021-8979(00)06613 -5].