Dynamic thermometry of a solid via optical diffraction method at pulsed irradiation

A method for the fast measurement of the temperature of solids under the action of a high-power light pulse is proposed and demonstrated. This method is based on the application of the Fraunhofer diffraction and is implemented for silicon samples heated to melting temperatures T _melt = 1412°C by a high-power light pulse. The current silicon temperature was determined by measuring the varying diffraction angle of the probing laser beam. The diffraction angle was varied over time because the period of the diffraction grating increased as a result of the dynamic thermal expansion of the crystal. An initial grating was formed on the surface of the silicon plate with a period of d = 4 μm. The radiation beam of a He-Ne laser with λ = 0.6328 μm was used as the probing beam; the measured signal was recorded in the pair of symmetric fifth-order diffraction maxima.