Ag2S quantum dots in the fields of picosecond and femtosecond UV and IR pulses: optical limiting, nonlinear absorption and refraction properties

We demonstrate strong optical nonlinearities of silver sulfide (Ag2S) quantum dots (QDs) in the ultraviolet range. The 4-nm Ag2S QDs were prepared by chemical method and analyzed using picosecond (800nm and 400nm, 200ps) and femtosecond (800nm and 400nm, 60fs) laser pulses. Our Z-scan measurements show that these QDs have large nonlinear absorption coefficient (10(-3) cm W-1) at 400nm. We also demonstrate the transient absorption and optical limiting in Ag2S QDs. Variations of the signs of nonlinear refractive indices and nonlinear absorption coefficients of QDs are demonstrated by changing pulse width and wavelength of probe radiation.