Center for Relativistic Laser Science

2019 16th Advanced Imaging Methods Workshop(AIM)

- Abstract :

"Near-field scanning optical microscopy (NSOM) is a useful tool for studying sub-diffraction nanostructures. As the size of nanostructures becomes smaller, the ability to observe and manipulate the near-field is getting more crucial. In ordinary NSOM imaging, the illumination of light source has not been a major concern since the spatial resolution is mainly determined by the collection process by the sub-wavelength aperture. 

We constructed a unique system that integrates far-field wavefront shaping by a spatial light modulator into an NSOM and developed methods to measure a far- to near-field transmission matrix (FNTM). Using the recorded matrix, we have demonstrated the manipulation of near-field waves and observation of the near-field eigenmodes generated by the nanostructures.

For the double-slot nanoantenna having the separation of 50 nm, which is about 13 times smaller than the wavelength of light source and 3 times smaller than the size of NSOM probe, we could obtain an anti-symmetric transverse mode which has a sharp phase singularity in the middle of the two slot antennas. This corresponds to the resolving of structures whose separation is smaller than the NSOM aperture. Moreover, by scanning the NSOM probe over the two-dimensional (2D) surface, we have demonstrated the mapping of 2D near-field eigenmodes for any arbitrary nanostructures. We believe that these studies exploiting the far- to near-field transmission matrix will open new venues for interrogating the complex nanophotonic structures."