Size-controlled quantum dots reveal the impact of intraband transitions on high-order harmonic generation in solids

Since the discovery of high-order harmonic generation (HHG) in solids1–3, much effort has been devoted to understand its mechanism and both inter- intraband transitions are known be essential1–10. However, affected by electronic structure a solid, how they contribute nonlinear carrier HHG remains an open question. Here we use mid-infrared laser pulses study CdSe CdS quantum dots, where confinement can used control transitions. We find that intensity per excited volume generated density increase when average dot size is increased from about 2 3 nm. show reduction sub-bandgap energy larger dots enhances transitions, this—in turn—increases rate photocarrier injection coupling with interband resulting enhanced HHG. Both high-harmonic solids, but their exact roles not fully understood. Experiments lead thus generation.