Improve optical modulation depth of terahertz wave by monolayers of plasmonic nanoparticles

Monodisperse colloidal gold nanoparticles were self-assembled into ultra-large-area monolayers and used as coating films on intrinsic silicon to improve the optical modulation depth of terahertz (THz) waves. The monolayer does not attenuate the transmission of THz wave but largely boost the generation of electron-hole pairs in silicon. The THz modulation depth of silicon was improved by a factor of 10 to 20 times for static modulation test with THz time domain spectroscopy upon laser irradiation power of 100 mW.