Short wavelength thermography: Theoretical and experimental estimation of the optimal working wavelength

Abstract

Radiometric temperature measurement methods, such as thermography, use mainly radiation in the infrared spectrum. In this wavelength range, applications are limited by the diffraction to macroscopic devices. The empirical optical resolution limit is given by the Rayleigh criterion. Given the interest in the study of thermal microsystems, we propose an optimization criterion taking into account both the thermal sensitivity and the signal to noise ratio of the considered radiometric methods. The optimization analysis results highlight the opportunity to reduce the working wavelength of thermography applications and, thus, improving the spatial resolution limit of the radiometric method used. This theoretical approach for wavelengths optimization of the radiometric methods is experimentally validated by a phase transition temperature measurement of a fused aluminium bath in both visible and near infrared spectral ranges.