Measurement of temperature distributions across laser heated samples by multispectral imaging radiometry.

Two-dimensional temperature mapping of laser heated diamond anvil cell samples is performed by processing a set of four simultaneous images of the sample, each obtained at a narrow spectral range in the visible to near infrared. The images are correlated spatially, and each set of four points is fitted to the Planck radiation function to determine the temperature and the emissivity of the sample, using the gray body approximation. The method is tested by measuring the melting point of Pt at 1 bar and measuring laser heated Fe at 20 GPa in the diamond anvil cell. The accuracy and precision are shown to compare well to standard spectroradiometry, and the effect of imaging resolution on the measured distribution is evaluated. The principal advantages of the method are (1) the temperature and emissivity of the sample are mapped in two dimensions; (2) chromatic aberrations are practically eliminated by independent focusing of each spectral band; and (3) all of the spectral images are obtained simultaneously, allowing temporal variations to be studied. This method of measuring temperature distributions can be generalized to other hot objects besides laser heated spots.