Abstract
The Transverse Photothermal Beam Deflection method for measuring thermal diffusivity (or thermal conductivity) is developed for and applied to samples with cylindrical geometry. The basic theoretical equations governing the absorption of the heating (pump) laser beam, the diffusion of the heat, and subsequent deflection of the probe laser beam in the refractive index gradient of the surrounding medium are derived. To demonstrate the theory, thermal diffusivities of selected metal wires are measured and compared to values of the diffusivity as derived from electrical resistance measurements. The pump beam is scanned along the length of the wire samples to measure the photothermal deflection signal as a function of distance along the long axis of the samples. From either the decrease in magnitude of the photothermal signal with distance along the wire, or the phase lag of the measured deflection with respect to the pump beam, the thermal diffusivity of the sample can be obtained. The advantages and disadvantages of determining the thermal diffusivity of thin cylindrical samples by this method are discussed.
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