Low power all-optical wavelength conversion with terahertz refresh rates using colloidal nanocrystals

Owing to their widely tuneable optical properties and strong light-matter interaction, colloidal quantum dots[1] (QDs) are considered for next-generation photonic devices such as solution processable lasers[2] and all-optical wavelength converters. Using QDs for this last application, i.e. wavelength conversion, is limited by either slow interband (106-109 s-1) or energy consuming multi-exciton dynamics (109-1012 s−1). Here we show, using white light pump-probe spectroscopy, that the interplay between two intrinsic material properties of PbS QDs, intraband absorption and interband bleach can lead to a very strong modulation of near-infrared light on an ultrafast, picosecond, timescale: A peculiar dynamic arises at the matching wavelength: a strong burst of absorption induced by the pump lasts for roughly 1 picosecond and vanishes, leaving the dots as they were before the pump pulse arrived.