Nonlinear spectroscopy of PbS quantum-dot-doped glasses as saturable absorbers for the mode locking of solid-state lasers

The bleaching relaxation characteristics of PbS quantum dots with diameters in the range of 3.8-4.3 nm synthesized in silicate and phosphate glasses have been studied under the conditions of femtosecond excitation. It has been observed that increase of pump fluence from 0.1 to 2.2 mJ/cm(2) leads to the appearance of a second (slow) component in the bleaching relaxation kinetics and to the shortening of both the fast (from several tens of picoseconds to several picoseconds) and slow relaxation times. An absorption saturation fluence of approximate to 15 mu J/cm(2) with a nonsaturable absorption coefficient of 2.5-3 cm(-1) at 1.05 mu m has been evaluated for the PbS quantum-dot-doped glasses studied. The nature of the nonsaturable absorption and the mechanism of the bleaching relaxation in PbS quantum dots have been discussed. (c) 2006 American Institute of Physics.