16 July 2014 Tracing the near field line

Vector field lines around an optical dipole antenna

Single molecule imaging with 40 nm response function

Single Molecule Dipole Maps the Local Vector Field of an Optical Nano-antenna In a recent study, Anshuman Singh and Gaëtan Calbris of the Molecular NanoPhotonics group led by ICREA Professor at ICFO Niek van Hulst have used single molecule “point” dipoles and a scanning optical antenna to map the 3D vectorial antenna field with 1 nm resolution and to achieve enhanced fluorescence imaging with 40 nm FWHM response. The work, supported by EU project NanoVista, was published in NanoLetters.

Optical antennas confine light on the nanoscale, enabling strong light-matter interactions and ultra-compact optical devices. Such confined nanovolumes of light have non-zero field components in all x-y-z directions. Now Anshuman Singh and colleagues have probed all 3 components of the local antenna field. To this end, they scanned a FIB-fabricated nanoantenna deterministically in close proximity to single fluorescent molecules, whose fixed excitation dipole moment reads out the local field vector. Thus a full vectorial mode map of all x-y-z-field components around a resonant antenna was obtained with nanometer molecular resolution.

They used the scanning resonant antenna for enhanced single molecule imaging with 40 nm FWHM response function. Out-of-plane molecules, almost undetectable in far-field, were made visible by the strong antenna z-field with excitation enhancement up to 100 times. Interestingly, the apparent position of molecules shifted up to 20 nm depending on the orientation of their dipole vector. The capability to resolve orientational information on the single molecule level makes the scanning resonant antenna an ideal tool for extreme resolution bio–imaging.