Center for Relativistic Laser Science

2019 IBS AOI Conference

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.

References

[1] Rotenberg, N. & Kuipers, L. “Mapping nanoscale light fields”. Nat Photonics 2014, 8, 919-926.

[2] Kim, M. et al. “Maximal energy transport through disordered media with the implementation of transmission eigenchannels”. Nat Photonics 2012, 6, 581-585.

[3] Kim, M., Choi, W., Choi, Y., Yoon, C. & Choi, W. “Transmission matrix of a scattering medium and its applications in biophotonics”. Opt Express 2015, 23, 12648-12668.

[4] Choi, W. et al. “Control of randomly scattered surface plasmon polaritons for multiple-input and multiple-output plasmonic switching devices”. Nat Commun 2017, 8.

[5] le Feber, B., Rotenberg, N., Beggs, D. M. & Kuipers, L. “Simultaneous measurement of nanoscale electric and magnetic optical fields”. Nat Photonics 2014, 8, 43-46.