Tiny antennas could bring the power of terahertz spectroscopy to bear on large molecules and other nanoscale objects.

Nanoantenna-enhanced terahertz spectroscopy (NETS) involves chains of dipole nanoantennas spaced about 20 nm apart. The technique builds on an existing strategy that has been successfully employed for other applications such as surface-enhanced Raman spectroscopy (SERS).

An international team of researchers led by professor Dr. Luca Razzari at the Canadian National Institute of Scientific Research (INRS) used NETS to retrieve spectroscopic data from a monolayer of CdSe quantum dots. Placed inside the antenna’s nanocavities, the QDs’ terahertz absorption was increased by more than a million times.

Although terahertz spectroscopy has applications in environmental monitoring and security screening, it previously could not be used effectively to study nanocrystals or molecules at extremely low concentrations. That’s because the relatively large wavelength of terahertz radiation — about about 300 µm at 1 THz — hinders its interaction with nanoscale objects.

NETS opens new research prospects in nanophotonics and broadens the field of applications in both spectroscopy and nonlinear optics, the researchers said.

Funding came from the National Science and Engineering Research Council of Canada and the Quebec Research Fund for Nature and Technology (FRQNT).

The research was published in Nano Letters (doi: 10.1021/nl503705w).

For more information, visit www.inrs.ca.