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Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful technique for a label-free identification of molecular species. The low infrared absorption cross sections of molecules are made up for the huge electromagnetic field enhancement provided by the resonant excitation of collective electron oscillations in metallic nanoantennas. Since these surface plasmons are localized at the nanometer scale, a minute amount of materials is detected leading to a weak SEIRA signal. The design of actual plasmonics detectors is a trade-off between the detection of very small volumes of molecules and the signal to noise ratio level. We demonstrate that an epsilon-near-zero (ENZ) material combined with nano-slits lifts this constraint and provides both extreme enhancement factor up to 107 and highly contrasted SEIRA signal for an extremely low amount of material of interest. These results are explained by the modification of the electromagnetic field of the gap plasmon mode sustained by the slits in the presence of the ENZ material. We propose to implement this concept with a semiconductor whose doping level engineering provides a versatile way to scan the whole molecules' fingerprint frequency range.

International audience; We propose an efficient optically actuated THz modulator based on an ultrathin epsilon-near-zero (ENZ) slab photogenerated in an InAs semiconductor. We experimentally demonstrate a modulation depth of 90% at 1 THz obtained with a continuous laser at irradiation lower than 10 W cm À2. Beyond the strong attenuation of the THz transmission provided by the ENZ absorption effect, we also report a broadband modulation of the THz waves from 1 to 10 THz. In addition, our experimental results show that the cutoff frequency of 3 dB attains 2 MHz in the dynamic modulation regime.

Active metasurfaces have attracted a great deal of attention due to the unlimited ways of controlling electromagnetic radiation. In this work, we theoretically study the THz electromagnetic properties of photogenerated metasurfaces in an InAs slab. We use a spatially modulated optical pump to modify the permittivity. Those modifications are calculated by solving the ambipolar rate equation for the photocarriers. This work reveals the crucial impact of the photocarrier diffusion for realizing optimal metasurfaces for the control of THz radiation. We demonstrate that InAs is a promising semiconductor that could be used to manufacture fast and efficient on-chip THz components. We also demonstrate that low pump fluence in the continuous regime of only tens of $\text{W}\phantom{\rule{0.16em}{0ex}}{\text{cm}}^{\ensuremath{-}2}$ is sufficient to modulate the absorption of the THz waves up to $67%$ over a broad frequency range from 1 to 3 THz.

The oxynitride materials present a high versatility, which enables their properties to be controlled by tuning their elemental composition. This is the case for silicon oxynitrides used for multilayer antireflective coatings (ARCs), where several thin films with various refractive indexes are needed. Different techniques allow for the modification of the thin film composition. In this paper, we investigate the reactive gas pulsing sputtering process to easily tune the thin film composition, from an oxide to a nitride, by controlling the averaged oxygen flow rate, without reducing the deposition rate, compared to a conventional reactive process (CP). We then demonstrated that the refractive indexes of films deposited by this pulsing process (PP) can be varied in the same range compared to films obtained by CP (from 1.83 to 1.45 at 1.95 eV), whereas their extinction coefficients remain low. Finally, the multilayer ARC has been simulated and optimized by a genetic algorithm for wavelength at 600 nm and for the silicon substrate. Various optimized multilayer (mono-, bi- and tri-layers) structures have been deposited by the PP technique and characterized. They are presented in good agreement with the simulated reflectivity. Hence, the PP allows for an easy depositing tri-layer system with a reasonable deposition rate and low reflectivity (8.1% averaged on 400–750 nm visible light range).

We propose a universal design which provides simple scaling laws that can be used as a recipe to realize ultra-thin perfect absorbers operating from infrared to microwave frequencies independently of the choice of the materials (i.e metal and dielectric) involved and for all polarization states of light.