Development of a novel probe for measuring emissivity and temperature during Raman spectroscopy

Abstract

Abstract In this work, an innovative tool to perform real-time measurements of emissivity and temperature of a given material surface under CW laser irradiation was developed. In the radiative energy balance, the emissivity represents the complementary component of the reflectance, thus, its measurement can be exploited to calculate the temperature at the target surface from infrared emission measurements provided by a suitable sensor. A miniaturized photothermal sensing line was designed as an accessory of Raman probes for driving thermal control loops in order to prevent overheating during the spectroscopic acquisition. To demonstrate its effectiveness and reliability, it was integrated with in a home-made Raman instrument (exc. 1064 nm) and associated software to achieve an automated online thermal control. Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its original spectral features. In several applications, 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 fingerprint. A thorough experimentation of the novel tool was carried out on photothermally sensitive materials such as red lead and massicot powders, traditionally used as pigments since ancient times. Finally, the compactness of the components and the fast response time made this system particularly suitable for nondestructive in-situ investigations.