In this work, we demonstrate that it is possible to use III-V semiconductors for plasmonics from the THz up to the midinfrared spectral range. We have fabricated hyperbolic nano-antenna based on heavily doped semiconductors demonstrating localized plasmon modes. This hyperbolic nano-antenna is 10 times: 10 nm doped InAs / 10 nm undoped GaSb. The free carriers are confined in the 10 nm layer of InAs. The confinement shifts the effective plasma frequency of the metamaterial towards the high frequencies, extending the possibility to probe molecules until 2000 cm-1 , thus covering the complete fingerprint frequency range for molecular and biosensing applications. The nano-structuration of the hyperbolic material allows to access two main plasmonic resonances at 800 cm-1 and 2000 cm-1 . This bimodal property is appealing to detect and identify biomolecules over a large spectral range. With these hyperbolic nanoantennas, we can either enhance the absorption of rovibrational modes of molecules with surface-enhanced infrared absorption (SEIRA) spectroscopy1 or enhance the thermal emission of molecules with surface-enhanced thermal emission spectroscopy (SETES)2
In this paper, III-IV semiconductors are demonstrated as strong candidates for plasmonics applications in the Mid-IR. The perfect absorbers (PA) fabricated with heavily doped semiconductors features strong coupling between Fabry-Perot and localized surface plasmon modes. Also, anisotropic nano-antenna fabricated at the top surface yield a huge anisotropy to the polarized light. The fabricated PA with 2D periodic arrays of rectangular nano-antenna is presented, where the rectangular shape allows one to excite localized surface plasmon resonances (LSPR) at different wavenumbers depending on the polarization of the incident light. Preliminary results of the bio-functionalization through phosphonic acid are shown for the PA aditionnally. Furthermore, it becomes clear that it is possible to detect bio-molecules of interest even far in the infrared on a very small surface and with a few hundreds of nano-antenna.
KEYWORDS: Raman spectroscopy, Lab on a chip, Signal to noise ratio, Optical fibers, Remote sensing, Spectrometers, Chemical analysis, Raman scattering, Molecules, Molecular spectroscopy
Raman spectroscopy (RS) is a non-destructive analytical technique, that provides a unique fingerprint of molecules with high accuracy. It proves to be a reliable and practical alternative to chemical analysis, allowing sample identification without the use of reagents. This label-free technique finds applications in quality control and in-line process monitoring, however, like any other technique RS also presents its challenges such as expensive and delicate instrumentation and complex design, which often confines the technique to the laboratory. In order to address these challenges, a 3D printed Lab-On-Chip (LOC) was fabricated and assembled with four channel optical fibres, which will collect the Raman scattering. The performance of our Raman Probe on Chip is evaluated using Isopropanol alcohol (IPA) as a validation sample.
The widespread use of smartphones forecasts huge increase in application-based portable sensors, particularly using the embedded light source and camera detector. Albeit Fibre Bragg gratings (FBG) were originally discovered at visible wavelengths, their commercial and scientific dissemination is predominant in the C-band of optical communications. Recently, several authors gave attention to FBG in the visible, aiming simpler and low-costly interrogation methods that could increase the application of FBG sensors in biomedicine, immunology and biophysics. We study the detection of VIS FBG using standard lamps or LEDs coupled to VIS, silicon based, CCDs in commercial instruments. We show that is possible to record the FBG spectrum with adequate signal to noise ratio,allowing hand held FBG interrogation methods in diverse environments.
A visible fiber Bragg grating (Vis-FBG) with wavelength peak centered at 673.07 nm was inscribed in a multimode fiber designed for infrared (IR) operation using a femtosecond (fs) laser emitting at 248 nm. The fiber cladding is removed by chemical etching in hydrofluoric acid solution (40%). The sensor refractive index response is determined by dipping the sensor into diluted glycerin solution at different concentrations with refractive index range from 1.3328 to 1.4607. The Vis-FBG performance is compared with an IR etched FBG (EFBG) with similar diameter. The sensitivity found for the Vis-FBG sensor is 15.71nm/RIU with a 6.34 x 10-3 RIU resolution for a refractive index of 1.4607.
Thermal sensitivity increase of regenerated fiber Bragg gratings (RFBG) in the visible range is reported. The FBGs are produced by direct illumination under the phase mask using UV light from two different laser sources at 248 nm. After regeneration the thermal sensitivity is obtained at 500°C to avoid spectra vanishing for temperatures near that of regeneration. At 500°C, the determined thermal sensitivities are 5.74pmK-1 before and 7.65pmK-1 after regeneration (single mode fiber in the visible, femtosecond laser), and a similar pattern is presented for all regenerated FBGs.
We report regeneration studies of fiber Bragg gratings with resonance band in the visible spectral range. The FBG were produced by direct illumination under the phase mask using UV light from a fs-laser pumped optical parametric amplifier. Some seed gratings were not so saturated as common C-Band gratings written by other methods but their regeneration efficiency is quite high. The final line-widths are narrower than the similar C-band regenerated gratings.
The thermal and deformation properties of fiber Bragg gratings (FBG) in the visible range were characterized for the first
time in our knowledge. The FBG were written in silica single mode (cutoff in the visible and infrared range) and
multimode fibers, using a phase-mask (460 nm period) illuminated by a 248 nm femtosecond laser.
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