Steady-state and transient microscale temperature measurements by multispectral method and photons counting

Highlights: • A three wavelengths pyrometer able to focus on a micrometric surface collects the photons emitted by this surface. • The wavelengths are selected according to several criteria and a global function takes into account the spectral parameters. • The photonic emission is a random phenomenon and the Gaussian law estimates an average photonic flux for each wavelength. • The temperature is estimated by a least-squares method from a multispectral pyrometer. - Abstract: This work presents steady-state and transient microscale temperature measurements by optical and multispectral method in the ultraviolet-visible wavelengths. Regarding the classic laws of radiative heat transfers, the photon counting is preferred to the energy measurement. The photonic emission is a random phenomenon and is here measured with statistical laws such as the Gaussian law. The spectral dependence of the optical apparatus transfer function is taken into account by a linear function and the temperature is estimated by inversion with a Levenberg–Marquardt algorithm. Measurements are performed with a small-dimension blackbody developed in the laboratory and with a Chromel wire. Both of them are capable of heating up above 1000 °C. The diameters of the observed surfaces are 10 µm and 5 µm, respectively. The theoretical criterion of wavelength selection and least-squares parameter estimation allow for a difference between the estimated and controlled temperatures lower than 4%.