Jacques Barbillat

Diffuse reflectance infrared spectroscopy: an experimental measure and interpretation of the sample volume size involved in the light scattering process

This work presents the second part of a basic study of diffuse reflectance spectroscopy through a comparison of experimental observations with existing theories of diffuse reflectance of non-absorbing powders. The diffusion volume approximate shape has been assumed to be a cylinder. Its dimensions have been measured for different non-absorbing powders with a refractive index from 1.4 to 3.4, and with different distributions of particle size larger than the wavelength. The lateral extension diameter Φm of this volume is at least two times larger than that of the irradiated sample surface. The variation of the cylinder height corresponding to the penetration depth, z∞, has a behavior opposite to that of the powder diffusion coefficient, S. Its variation with the mean particle diameter is smaller than predicted by the theories. For KBr, a 1 mm thick layer can be considered as a semi-infinite layer. Comparison between existing theories of diffuse reflectance of powdered samples, shows that the statistical theories explain a good deal of the experimental observations concerning their variation with the particle parameters. This comparison shows a similarity between attenuated total reflection and diffuse reflectance spectra. Nevertheless, some discrepancies still persist; this may be due to the fact that the side-way scattering, which may be related to light transfer between neighbouring rough particles by frustrated total reflection, has only been indirectly taken into account.

Near infra-red Raman spectroscopy with dispersive instruments and multichannel detection

Abstract We describe in this paper the development of multichannel dispersive Raman microprobes using near infrared excitation beyond 1000 nm and linear array detectors offering good sensitivity in the near infrared region of the spectrum between 1000 and 1600 nm (Germanium and Indium-Gallium-Arsenide photodiodes) and we complete these results with those obtained on the same instruments with silicon based CCD detectors and red or infrared excitation. We demonstrate that such instruments are useful for the investigation at the microscopic level or for remote analysis by means of optical fibres of samples which fluoresce under visible illumination. Raman data of various samples collected on these Raman microprobes with either a Ge or an InGaAs photodiode array or a silicon based 2D CCD are presented.

Optimisation of the chemical generation of singlet oxygen (1O2, 1Δg) from the hydrogen peroxide–lanthanum(III) catalytic system using an improved NIR spectrometer

A near-IR chemiluminescence spectrometer designed to study chemical sources of singlet oxygen ((1)O(2), (1)Delta(g)), was built by coupling a reactor compartment to a nitrogen-cooled Ge diode through a bundle of optical fibres. This device was used to optimise the generation of (1)O(2) from the hydrogen peroxide-lanthanum(iii) catalytic system. The reaction kinetics were studied with a 2(3)3(3)//12 screening experimental design comprising twelve experiments. The influence of six factors was examined: the nature of the lanthanum salt (hydroxide, oxide or nitrate) and its concentration (0.05 or 0.1 mol L(-1)), the pH value (5, 7 or 9), the concentration of H(2)O(2) (0.5, 1 or 2 mol L(-1)), the temperature (20 or 30 degrees C) and the concentration of EDTA (0 or 5 mmol L(-1)). Two responses were measured: the rate of H(2)O(2) disproportionation and the intensity of the luminescence of (1)O(2) at 1270 nm. The essential factor is the nature of the lanthanum salt since La(NO(3))(3) induces the disproportionation of H(2)O(2) about 60 x faster than La(2)O(3) or La(OH)(3). Other influencing factors are the pH value, the concentration of H(2)O(2), the temperature and the concentration of the lanthanum salt whereas the concentration of EDTA has no effect on the reaction. The catalytic activity of La(NO(3))(3) was then investigated in further detail by studying the influence of two factors (pH and [H(2)O(2)]) thanks to a Doehlert design.

4 – Raman Imaging

Publisher Summary This chapter focuses on the several techniques of Raman imaging. Raman imaging methods can be classified in two categories: “parallel- or direct-imaging” or “series-imaging” techniques. The direct-imaging technique results in the immediate production of a complete two-dimensional (2D) image at a chosen wavelength which is characteristic of a molecular compound within the fully illuminated specimen. It necessarily requires a 2D detector. Series-imaging techniques require image reconstruction, which is achieved either by scanning the sample with a finely focused laser beam or by encoding with a mask the image of the sample illuminated by an expanded laser beam. Although single-element detectors can be used for image reconstruction, the best results are obtained with 2D multichannel detectors such as a charge-coupled device (CCD) detector. The chapter discusses the performance comparisons between Hadamard imaging, global illumination and line scanning. Direct imaging gives a better signal-to-noise ratio (S/N) and Hadamard imaging is preferred over direct imaging only in the case of very low signal levels. The global-illumination techniques provide much more total laser power at the sample than do scanning techniques, although each pixel of the sample does not receive more energy.