Research

Nonlinear and ultrafast photonics

What happens to light and matter on femtosecond timescales in an extreme field?

Extreme confinement creates enormous fields, gradients, and energy densities in nanoscale volumes. In our nanogap cavities, a few nanometers of ordinary dielectric become an efficient source of harmonic generation; several nonlinear processes can be driven and controlled in a single cavity at once; and a material with no second-order response in the bulk, diamond, becomes a bright source of second-harmonic light. Arrayed into metasurfaces, the same cavities become devices — ultrafast thermal detectors, surfaces whose light–matter coupling can be tuned in real time, nanoscale frequency converters.

What happens in the first femtoseconds after light enters such a structure is largely unexplored. We are building a femtosecond pump–probe laboratory, coupled to single-photon detection, to follow how energy moves through these systems from the moment of excitation, and to change the cavity — and the vacuum it defines — faster than the matter inside it can respond: shaping photon wavepackets in time, switching light–matter coupling on and off, and, ultimately, creating photons from a vacuum that is modulated faster than an optical cycle.

Key papers

• A metasurface-based diamond frequency converter using plasmonic nanogap resonators
  Q. Shen, A. Shams-Ansari, A. M. Boyce, N. C. Wilson, T. Cai, M. Loncar, M. H. Mikkelsen, Nanophotonics 10, 589–595 (2021) · DOI
• Active control of multiple, simultaneous nonlinear optical processes in plasmonic nanogap cavities
  Q. Shen, W. Jin, G. Yang, A. W. Rodriguez, M. H. Mikkelsen, ACS Photonics 7, 901–907 (2020)
• Probing the origin of highly-efficient third harmonic generation in plasmonic nanogaps
  Q. Shen, T. B. Hoang, G. Yang, V. D. Wheeler, M. H. Mikkelsen, Optics Express 26, 20718–20725 (2018)
• Real-time tunable strong coupling: from individual nanocavities to metasurfaces
  J. Huang, A. J. Traverso, G. Yang, M. H. Mikkelsen, ACS Photonics 6, 838–843 (2019)
• Ultrafast pyroelectric photodetection with on-chip spectral filters
  J. W. Stewart, J. H. Vella, W. Li, S. Fan, M. H. Mikkelsen, Nature Materials 19, 158–162 (2020) · DOI
• Metasurface-enhanced thermal photodetector operating at gigahertz frequencies
  E. Shin, R. E. Bangle, N. C. Wilson, S. B. Nikodemski, J. H. Vella, M. H. Mikkelsen, Advanced Functional Materials 36, 2420953 (2026)
• Actively tunable metasurfaces via plasmonic nanogap cavities with sub-10 nm VO2 films
  A. M. Boyce, J. W. Stewart, J. Avila, Q. Shen, S. Zhang, V. D. Wheeler, M. H. Mikkelsen, Nano Letters 22, 3525–3531 (2022)