Published online by Cambridge University Press: 15 February 2011
A modification of the transverse photothermal deflection technique is used to determine the thermal diffusivity of high-conductivity carbon fibers. A chopped, cw Ar-ion laser beam is focused to a point on the fiber to cause localized heating of the fiber and the surrounding transparent fluid medium. The fluid medium immediately adjacent to the fiber sample is probed with a weak He-Ne laser that grazes the fiber surface and is deflected by the synchronous thermal lens produced near the fiber surface. The pump laser is stepped along the length of the fiber to produce a photothermal signal that is proportional to the temperature gradient along the length of the fiber. The theory necessary to predict the magnitude and phase of the probe beam deflection as a function of distance along the fiber is derived. This signal can then be analyzed by a simple method to determine the thermal diffusivity of the carbon fiber.