Heavily Doped Semiconductor Colloidal Nanocrystals as Ultra-Broadband Switches for Near-Infrared and Mid-Infrared Pulse Lasers.

Heavily self-doped semiconductors can be designed to be used in advanced photonics due to both fabrication and functional advantages. Ultrafast response, strong optical nonlinearity, broadband wavelength range, and accessibility of integration are major challenges for ultrafast all-optical photonics to operate in the infrared wavelength range. Here, solution-processed CuSe semiconductor nanocrystals (NCs) demonstrate an ultrafast response (about 360-520 fs), strong optical nonlinearity (as large as -1.4 × 10 cm GW), and broadband (from 800 to 3000 nm) nonlinear optical absorption in the near-infrared and mid-infrared wavelength ranges. The ultrafast response and larger optical nonlinearity may be triggered by the plasma ground-state bleaching in the strong surface electromagnetic filed. Stable Q-switched lasers in Er-doped fiber laser, Tm-doped fiber laser, and Ho/Pr-codoped ZBLAN fiber laser are operated, respectively. These findings indicate that CuSe NCs are prospective nonlinear materials for ultrafast response and broadband pulse laser.