Prof.  Benfeng  Bai
Tsinghua University,  China

Title: Frontiers in near-field optics: from ultraprecision manufacturing to multi-physics measurement

Abstract:

Near-field optics is a frontier field in nanophotonics and plasmonics, which focuses on the study of light-matter interaction in the close vicinity (usually within one wavelength above the surfaces) of nanostructures or materials, where the electromagnetic field components carrying high spatial frequency information exist in evanescent form and may interact strongly with nano-objects. In this talk, we review and demonstrate our recent research advances in developing novel near-field optical techniques to achieve ultraprecision nanofabrication and nanomeasurement. Specifically, a method called optical far-field-induced near-field breakdown (O-FIB) approach is developed, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting “knife edge” is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (~λ/40) is readily achieved and the polarization control of the incident light can steer the nanogroove writing along the designed pattern. Then, we show some new advances in scanning near-field optical microscopy (SNOM) to realize multi-field characterization of nanomaterials and nanostructures. A general near-field imaging theory based on the reciprocity of electromagnetism is established, which reveals the mechanism of probe-field interaction and can be a tool for designing functional nanoprobes. By employing the theory and combing ultraprecision measurement techniques, several new near-field microscopic methods have been developed, including a spin-selective and phase-resolved SNOM that can directly probe the photonic spin-orbit interactions in nanoscale, a scattering-type SNOM that can probe the nonlinear response of nanomaterials excited by confined modes, a nano-photoluminescence microscopic method that can sensitively and accurately discriminate various nanodefects in low-dimensional materials through exciton emission imaging, and a brand-new method called light enhanced van der Waals force microscope (LvFM) that can discriminate the nanoscale heterogenous composition of nanomaterials with a very high spatial resolution far below the diffraction limit under ambient conditions. The proposed methods and systems provide powerful tools for the exploration of light-matter interactions in novel nanomaterials such as low-dimensional materials.

Biography:

Professor Benfeng Bai is the principal investigator of the Nanophotonics Group in the Department of Precision Instrument in Tsinghua University with research emphases on Advanced Nano-devices, Nano-fabrication and Nano-measurement based on Near-field Optics. He has published 100+ research papers in leading journals including Nature Communications, Light: Sci. & Appl., Nano Letters, Advanced Functional Materials, etc., has given 20+ invited talks in international conferences, and has been granted 30+ patents. He is now the board member of many academic organizations such as the Sino-French Optoelectronics and Photonics International Research Network (PHOTONET) and the National Technical Committee on Standardization of Nanotechnology of China. He has been a Topical Editor for Optics Letters (2014-2020) and is now a board member of journal Micromachines.