Charlie Koechlin

Wideband omnidirectional infrared absorber with a patchwork of plasmonic nanoantennas

In this Letter, we demonstrate experimentally that a patchwork of four metal-insulator-metal patches leads to an unpolarized wideband omnidirectional infrared absorption. Our structure absorbs 70% of the incident light on a 2.5 μm bandwidth at 8.5 μm. It paves the way to the design of wideband efficient plasmonic absorbers in the infrared spectrum.

Total routing and absorption of photons in dual color plasmonic antennas

We present both theoretical and experimental evidence that two metal-insulator-metal plasmonic resonators can be combined into a wideband and total photon absorber in the mid-infrared. We show that, although closely arranged in a subwavelength period, these resonators behave as angularly independent antennas at their own resonant wavelength. The structures thus allow for an efficient dual color photon routing and collection.

Analytical description of subwavelength plasmonic MIM resonators and of their combination.

We show that a periodic array of metal-insulator-metal resonators can be described as a high refractive index metamaterial. This approach permits to obtain analytically the optical properties of the structure and thus to establish conception rules on the quality factor or on total absorption. Furthermore, we extend this formalism to the combination of two independent resonators.

Electrical characterization of devices based on carbon nanotube films

Statistical study of electrical conduction on a large array of devices based on carbon nanotube films shows a weakly dispersive film conductivity, and a specific contact resistance of 1.1 10−6 Ω cm2, which is four orders of magnitude lower than previously reported values. This allows identifying the conductivity of the carbon nanotube films as driven by a fluctuation induced tunneling mechanism. Such results pave the way to the realization of optoelectronic devices, such as highly sensitive light or gas sensor arrays.

Complex optical index of single wall carbon nanotube films from the near-infrared to the terahertz spectral range

We retrieve the complex optical index of single-walled carbon nanotube (CNT) films in the 0.6-800 μm spectral range. Results are obtained from a complete set of optical measurements, reflection and transmission, of free-standing CNT films using time domain spectroscopy in the terahertz (THz) and Fourier transform infrared (IR) spectroscopy in the visible-IR. Based on a Drude-Lorentz model, our results reveal a global metallic behavior of the films in the IR, and confirm their high optical index in the THz range.

Potential of carbon nanotubes films for infrared bolometers

We investigate in this paper the potential of carbon nanotubes for infrared bolometers. A method to obtain CNT film layer and technological processes to obtain matrix of devices are presented. The electrical characterization of samples establishes the quality of our technology i.e. low contact resistance, and weak dispersion between devices. The potential of carbon nanotubes films as bolometric material is investigated by measuring the thermal dependence of their resistance and by comparison with amorphous silicon (one of the leading material for bolometric applications). Optical measurements of CNT films in the infrared and THz ranges show a relatively high absorption for a few hundreds nanometers thick material. Eventually the infrared (8-12 μm) photo-response of a first demonstrator is presented and discussed.

Plasmonic nano-antennas for spectral emissivity engineering

We demonstrate experimentally that plasmonic nanoantennas made of metal-insulator-metal ribbons can be used to tailor the spectral emissivity of a gold surface in the infrared. Two areas of a gold mirror sample were covered with various combinations of nanoantennas. Their emissivity was characterized thanks to a dedicated bench, based on the combination of a Fourier transform spectrometer and a microbolometer infrared camera. A near unity polarized emission on two distinct infrared bands is obtained on the respective two areas, which is coherent with theoretical predictions.

Funneling of light in combinations of metal-insulator-metal resonators

We show both theoretically and experimentally that metal-insulator-metal resonators can be combined within the same subwavelength period and still behave independently. This permits to conceive surface with customizable absorption, which can for instance be used in dual band absorber or in omnidirectional wideband absorber. An energetic analysis can also be applied on these more complex antennas geometries, which highlights a sorting effect: at each resonance wavelength, the photons are funneled towards the apertures of the corresponding MIM cavity.