Optical switching spectroscopy of PbS quantum dots with dual-wavelength pump–probe

Optical transmission modulation in PbS quantum dots is investigated using a dual-wavelength pump–probe technique. High-energy excitation at View the MathML source efficiently alters the transmission of a probe beam 1100–View the MathML source spectral range, with a clear enhancement observed at longer wavelengths towards the exciton peak View the MathML source. A decay time of less than View the MathML source is measured for pump intensities of up to View the MathML source. The maximum modulation is delayed by approximately View the MathML source relative to the perfect overlap of the pump and probe pulses, the time required for the electrons to reach lower energy states. Long-term exposure shows photodegradation but the process is reversible and recovers on its own after several hours.