Raman spectroscopy and UV pulsed laser: an excellent symbiosis?

Abstract

The fundamental idea of the present work concerns photon technology performance. On the one hand, in order to improve the Raman spectral quality when pigment analysis is carried out, we use UV pulsed laser radiation (266 nm) and its non-thermal photoablation-induced effect. In this way, the unwanted superficial layers (old varnishes, for example, in easel paintings) can be locally removed and so a reduction of the total fluorescence in the spectrum of the analyzed zone is achieved. On the other hand, for the purpose of analyzing the quality of the process, we employ Raman spectroscopy to obtain molecular information about the previous and later compositions of the surface irradiated with UV pulses. The fluorescence reduction of the Raman spectra and its consequent spectral quality improvement are quantified by a proposed figure of merit (signal-to-noise ratio) which is calculated in a suitable spectral range. The UV pulses are obtained starting an Nd : YAG pulsed laser (1064 nm) in combination with non-linear optical crystals, and the Raman system used in the analytical measurements is a Jobin Yvon Induram with optical fiber technology and an He-Ne continuous laser (632.8 nm). A Haas shutter guarantees the spatial focusing of the optical pulses over a concrete point of the irradiated sample. Based on the experimental results, two conclusions can be established: first, non-thermal photoablation is very effective at removing small areas of the superficial varnished layers; second, Raman spectroscopy and the proposed figure of merit are very useful for measuring the resulting improvement in spectral quality.

The role of mobile instrumentation in novel applications of Raman spectroscopy: archaeometry, geosciences, and forensics

“…Good databases need to be developed [8][9][10][11][12][13][14][15][16] and searching algorithms are crucial. [106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121] When studying degradation phenomena, Raman spectroscopy has been combined with the evaluation of thermodynamic equilibria. [65][66][67] For the analysis of ceramics, glazes and glass, often spectra are deconvoluted and band positions and band widths are used to determine the supramolecular structure in the silicate phase.…”

Raman spectroscopy in art and archaeology

“…Examples of this approach are given by Rosi et al 6 and Ricci et al 7 The combination of Raman spectroscopy and scanning electron microscopy is discussed by Galli et al 8 Proton-induced X-ray emission (PIXE) is another option for elemental analysis, which can be combined with Raman spectroscopy. 9,10 In the paper by Ruiz-Moreno et al, 11 fluorescence spectroscopy is tested as a complementary technique for the analysis of pigments.…”

Optimum acquisition of Raman spectra in pigment analysis with IR laser diode and pulsed UV irradiation

“…Here, as an indicator of the information content, we use a methodology previously demonstrated in Ref. 11, which is based on the integrated value (area) of one or more Raman bands. 5…”

“…Our objective is to estimate the information and the total noise in order to integrate the mean square values of these components (signal and noise) in an effective spectral width. 11 Then, by means of the usual signal processing techniques (smoothing or averaging), we can obtain, first, an estimation of the statistical average of the Raman spectrum and, second, a polynomial approximation of the fluorescence base line. We denote these magnitudes as < E x > and < F x >, respectively, as in Fig.…”