Plasmonic Graded Gratings for Hyperspectral Near-field Infrared Sensing and Imaging

Arthur O. Montazeri Chemical and Biomolecular Engineering, University of California - Berkeley, Berkeley, California, USA Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada Michael Fang Chemical and Biomolecular Engineering, University of California - Berkeley, Berkeley, California, USA Physics, University of California - Berkeley, Berkeley, California, USA Hoi-Ying Holman Berkeley Synchrotron Infrared Structural Biology, Lawrence Berkeley National Laboratory, Toronto, California, USA Roya Maboudian Chemical and Biomolecular Engineering, University of California - Berkeley, Berkeley, California, USA Carlo Carraro Chemical and Biomolecular Engineering, University of California - Berkeley, Berkeley, California, USA Nazir Kherani Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada

Patterning a metal-dielectric surface with properly arranged subwavelength features provides the means for light to excite surface plasmon polaritons (SPPs) [1]. However, these creases, or other indentations of the surface can become more than just a means for SPP excitation. Indeed, these features could become resonant cavities, waveguides, or a combination thereof, extending in one, two or three dimensions. They can be functionally graded through spatial tapering of their pertinent geometrical parameters. (See Fig. 1 (a)) E.g. these subwavelength grooves can act as resonant waveguides with no cut-off for certain cavity modes and polarizations [2]. As a result, even in the spectral ranges where SPPs do not form on flat metallo-dielectric boundaries (λ > mid-IR), these subwavelength features can give rise to SPP-like behavior, known as “spoof SPPs” [3].

One aspect of these subwavelength grooves (See Fig. 1 (b) or (c)), is that when the groove-width is comparable to the evanescent tail of the SPP, it can result in SPP-coupling. The narrower the groove becomes, the stronger this coupling. We show that a far more practical approach is to use this property alone to create frequency selective surfaces without changing the groove-depth.

Fig. 1: (a.) Illustrates the emergent “rainbow-trapping” on a system of weakly-coupled grooves each housing strongly-coupled SPPs (b.) The E-field simulation of a graded-grating trapping localized infrared wavelength at λ = 6 µm (c.) An application example: utilizing this substrate as a platform for low-phototoxicity infrared spectroscopy in biological tissue.

This approach is a powerful tool for facile design of hyperspectral surfaces without the need for full wave simulation.

References:

[1] J. B. Pendry, et al., Science, vol. 305, no. 5685, pp. 847–848 (2004).

[2] J. Le Perchec, et al., Physical Review Letters 100, (2008).

[3] A.O. Montazeri, M. Fang, P. Sarrafi, and N.P. Kherani, arXiv 1406.3083v2 (2015)

arthur.montazeri@berkeley.edu