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Optical transmission modulation in PbS quantum dots is investigated using a dual-wavelength pump-probe technique. High-energy excitation at 800 nm efficiently alters the transmission of a probe beam 1100-1600 nm spectral range, with a clear enhancement observed at longer wavelengths towards the excitation peak (2100 nm). A decay time of less than 2.5 ps is measured for pump intensities of up to 3.8 GW/cm2. The maximum modulation is delayed by approximately 1 ps 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 by the process is reversible and recovers on its own after several hours.
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