Novel Probe for Thermally Controlled Raman Spectroscopy Using Online IR Sensing and Emissivity Measurements

Abstract

Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its characterization. Thus, such photothermal side effects can represent a serious problem to be carefully controlled in order to safeguard the integrity of the material and its spectral features. In this work, an innovative probe for thermally controlled portable Raman spectroscopy (exc. 785 nm) equipped with infrared sensing lines was developed. It included an infrared source and two thermopile sensors, which allowed to perform real-time measurements of the local emissivity of the material surface under laser excitation. The emissivity, which is needed in order to monitor the temperature of the irradiated surface through infrared radiation measurements, represents the complementary component of the reflectance in the radiative energy balance. Thus, total reflectance, temperature measurements and Raman spectroscopy were integrated in the present probe. After independently assessing the reliability of the former in order to derive the emissivity of variety of materials, the probe was successfully applied on pigments, paint layers, and a painting on canvas. The results achieved evidence the significant exploitation potential of the novel tool.

Time and spatially resolved VIS-NIR hyperspectral imaging as a novel monitoring tool for laser-based spectroscopy to mitigate radiation damage on paintings

“…The different behavior of the pigment powder and the oil paint of the same pigment may suggest a better heat dissipation of the oil binder, which was suggested also in another study. 24 This comparison highlights how important it is to study the laser interaction of the pigments in the specific binding medium of interest, to avoid misleading conclusions on the potential damage.…”

“…A very useful monitoring method has been designed by Mencaglia et al 23,24 that enables adjustment of the Raman laser power based on simultaneous thermal monitoring of the irradiated surface. However, the fundamental limitations are that thermal damage thresholds of materials are not always known a priori, and laser-induced alterations may not always result in a significant increase of surface temperature, e.g., photochemically dominated reactions.…”

Feature Papers in Optical Sensors 2022

“…In the tenth paper, by Calvagna et al [ 10 ], an innovative probe for thermally controlled portable Raman spectroscopy (exc. 785 nm) equipped with infrared sensing lines was developed.…”