Mid-Infrared (mid-IR) spectral range, spanning from 2 μm to 20 μm, is ideal for chemical sensing using spectroscopy thanks to the presence of vibrational absorption bands of many liquid and gas substances in this wavelength range. Indeed, mid-IR spectroscopy allows simultaneous qualitative and quantitative analysis by, respectively, identifying molecules from their spectral signature and relating the concentrations of different chemical agents to their absorption coefficient according to Beer-Lambert law. In the last years, photonic integrated sensors based on mid-IR spectroscopy have emerged as a cheap, accurate, and compact solution that would enable continuous real-time on-site diagnostics and monitoring of molecular species without the need to collect samples for off-site measurements. Here, we report the design, processing and characterization of a photonic integrated transducer based on selenide ridge waveguides. Evanescent wave detection of chemical substances in liquid phase (isopropyl alcohol, C<sub>3</sub>H<sub>8</sub>O, and acetic acid, C<sub>2</sub>H<sub>4</sub>O<sub>2</sub>, both dissolved in cyclohexane) is presented using their absorption at a wavelength of 7.7 μm.
Development of Mid-infrared sensors for the detection of biochemical molecules is a challenge of great importance. Mid-infrared range (4000 – 400 cm<sup>-1</sup>) contains the absorption bands related to the vibrations of organic molecules (nitrates, hydrocarbons, pesticides, etc.). Chalcogenide glasses are an important class of amorphous materials appropriate for sensing applications. Indeed, they are mainly studied and used for their wide transparency in the infrared range (up to 15 μm for selenide glasses) and high refractive index (between 2 and 3). The aim of this study is to synthesize and characterize chalcogenide thin films for developing mid-IR optical waveguides. Therefore, two (GeSe<sub>2</sub>)<sub>100-x</sub>(Sb<sub>2</sub>Se<sub>3</sub>)<sub>x</sub> chalcogenide glasses, where x=10 and 50 were chosen for their good mid-IR transparency, high stability against crystallization and their refractive index contrast suitable for mid-IR waveguiding. Chalcogenide glasses were prepared using the conventional melting and quenching method and then used for RF magnetron sputtering deposition. Sputtered thin films were characterized in order to determine dispersion of refractive index in UV-Vis-NIR-MIR. Obtained results were used for the simulation of the optical design in mid-infrared (λ = 7.7 μm). Selenide ridge waveguide were prepared by RIE-ICP dry etching process. Single-mode propagation at 7.7 μm was observed. Optical losses of 0.7 ± 0.3 and 2.5 ± 0.1 dB.cm<sup>-1</sup> were measured in near-infrared (λ = 1.55 μm) and midinfrared (λ = 7.7 μm), respectively. Achieved results are promising for the fabrication of an integrated optical sensor operating in the mid-infrared.
This paper reports the development of a sensor based on surface-enhanced Raman scattering (SERS) for analyses in seawater.
Polycyclic aromatic hydrocarbons (PAHs) are targeted by these sensors and their detection in situ summons up
chemical synthesis and optical development. Firstly, a relevant synthesis of SERS active substrates based on gold
nanostructures is presented. Different kinds of substrates have been synthesized under variable experimental conditions
to modify some parameters such as i) gold shape, size and distribution and such as ii) chemical functionalization: (i) gold
nanoparticles were prepared either by chemical reduction of HAuCl<sub>4</sub> or by physical deposition. (ii) Substrates were
functionalized by hydrophobic films to allow nonpolar molecules pre-concentration. Low concentration from ppb to ppm
of PAHs were detected with a Raman microscope designed for lab experiments. Sensors exhibit strong enhancement of
Raman scattering from molecules adsorbed on the films. Spectra were recorded for two PAHs (naphthalene and pyrene)
in artificial sea-water with limits of detection of 10ppb for both with a short integration time (10s) and a low incident
laser power (~0.1mW). Active substrate surface morphology was characterized with scanning electron microscopy
(SEM) measurements. Secondly, an home-made in situ Raman spectrometer was developed and has been connected to a
micro-fluidic system. This system was designed to host SERS-active sensors in order to ensure measurements with a
flow cell. This original configuration of in situ Raman spectroscopy was then achieved. Such a device is now ready to
use to confirm the PAH detection at ppb levels during the offshore experiments thanks to SERS sensors.