Multiple methodologies and experimental devices are developed in view of providing original spectroscopic tools suitable for the physical-chemistry investigations of materials, interfaces, nanomaterials and molecules. They include original imaging modes, experimental configurations coupling different techniques and various environmental cells as well as improved spectroscopic techniques, patented prototype instruments and novel optical materials.

Non-linear optics

Thanks to a tunable ps laser source, we developed a unique third harmonic scattering technique in condensed media, in addition to second harmonic scattering (hyper-Rayleigh). Thus, we were able to carry out original physicochemical analyzes, by combined second and third harmonic scattering on molecules and nanoparticles. More generally, these are new multimodal approaches in non-linear, electronic and vibrational optical spectroscopies. Thus, very recently, for the first time in the world, we have demonstrated a new molecular chiroptic technique: hyper-Rayleigh optical activity (HROA). We have also developed and perfected in recent years correlative imaging technique that couples the Raman signal (giving structural information) to the second harmonic response (SHG) (giving structural and / or space charge type non-linear optical information), which was particularly decisive for the study of many systems, such as thermally polarized glasses. This enabled us to initiate a Laphia Passport "Protein-Crystal Multimodal Imaging" technology transfer project (2014-15), carried out in collaboration with the company Explora Nova and B. Kaufman (IECB, UBx). In this context, we have developed an ultra-fast bimodal 3D meso-imager prototype (dual scanning mode) allowing us to combine large size SHG images (typically 200µm × 200µm × 500µm) at 1064 nm and in white light. We are currently finalizing the coupling with Raman Stokes spectroscopy at 1064 nm (spectral trimodality), from the same laser source used for SHG.

Enhanced Raman spectroscopy

Our AFM-based tip-enhanced Raman spectroscopy (TERS) transmission instrument has been supplemented with several new functions. The addition of a device allowing the injection of a white light in total internal reflection (TIR) made it possible to carry out colocalized measurements by AFM, conventional Raman (and surface-enhanced Raman scattering, SERS) spectroscopy and dark-field Rayleigh scattering microscopy (DFRSM). This technique was used to characterize the plasmonic properties of noble metal nanoparticles (monomers, dimers and TERS probes). This setup was also adapted to excite nanostructures with an evanescent field produced by laser irradiation in TIR configuration, and follow for instance the dynamics of a molecular substitution reaction on silver nanowires active in SERS. This TIR-SERS technique was the prelude of the on-going development of the TIR-TERS one for which the TERS probe is then excited by the evanescent wave, this TERS configuration ensuring higher electromagnetic exaltation than traditional experimental geometries.

Raman Optical Activity

In order to be able to probe the Raman Optical Activity (ROA) of CH, OH, NH elongation, combination modes and harmonics at high frequencies (impossible with commercial ROA spectrometers), we have developed a new Raman method called Multispectral Composite Raman spectroscopy allowing them to be reached efficiently. Adaptable to any type of Raman spectrometer, this invention was awarded Fast Track project funding by Aquitaine Science Transfert in 2017, protected by a patent in 2018 [Patent FR 3081221], and resulted in the development of a portable industrial Raman demonstrator operating in the near infrared from 100 to 7000 cm-1 with almost constant resolution and detectivity.

Fluorescence for prevention of fraud

We have developed a prototype portable, small size, low weight and autonomous fluorescence spectrometer to detect possible counterfeit spirits in a non-destructive way by performing an analysis of the liquid directly through the bottle [Patent FR 3039650]. For example, by irradiating a cognac with laser excitation at 514 nm, an intense fluorescence emission is observed, the maximum of which is located at 623 nm. Under the same conditions, the fluorescence emission of a fake cognac is less intense with a maximum around 606 nm. The fluorescence signals of the two samples are therefore significantly different in shape, which ensures the identification of counterfeits.

Micropoled glasses

A new method of manufacturing micro-structured optical surfaces was developed and supported by three transfer of technology maturation projects. The patented thermo-electrical imprinting process allows patterning of gradients of refractive index, as well as second order optical responses. Used on optimized glassy compositions for visible and IR spectral ranges, linear and non-linear optical properties can be inscribed at the micrometer scale over large surfaces (up to a classical wafer scale). Our current objectives are linked to the conception of (i) matrices of micro lenses for the mid IR and (ii) electro-optical amorphous niobate waveguides for photonic integrated circuits.

Raman, Neutron and IR spectroscopies in a controlled environment

As part of a collaboration between the group and the Laboratory Léon Brillouin, a high-resolution portable Raman spectrometer equipped with a fiber sample can allowing injection and optical collection as well as filtering of the scattered signal was developed. This can adapted to standard orange cryostat made it possible to perform coupled Raman spectra and neutron scattering measurements on systems under controlled temperature and pressure. Moreover, an environmental cell (ensuring the control of the exposure atmosphere, and in particular the humidity, of individual particles of size less than 100 μm) suitable for a commercial acoustic levitation device was designed and successfully coupled to a Raman microspectrometer (support from CNRS, Interdisciplinary mission). The subsequent implementation of rapid imaging on this spectrometer enabled Raman imaging of a levitating particle under in situ and operando conditions (SPECAERO Region Project). Coupling with mass spectrometry, to follow both the condensed and gas phases of individual organic particles, is under development in collaboration with the EPOC laboratory (UMR CNRS 5805 - CNRS INSU). Finally, an accessory allowing IR absorption measurements in ATR mode (with germanium or silicon crystal) at high pressure (10 MPa) and at high temperature (150°C) was also developed.