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In this work, we present a photothermal technique that measures at microscopic spatial scales the curvature of the surface of the sample due to the thermal expansion produced by a focused modulated laser beam. A modulated pump beam heats the sample surface and a probe beam delivered through the same optical fiber and slightly defocused probes the curvature, by analyzing the power collected by the same optical fiber. The collected power depends on the defocusing produced by the curvature of the surface induced by the thermal expansion. The phase delay is directly related to the thermal diffusivity of the sample at the impinging location. The scheme is based on the use of photonic technology borrowed from the optical communications field. In this way, the setup results extremely robust, both lasers (pump and probe) are inherently collinear, as they emerge from the same single mode fiber, and the detection is made through the same optical fiber.

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Abstract-A simple semiempirical model of the electron beam generated by a pulsed cold cathode electron gun has been developed. The model describes analytically the observed self-focusing of the discharge and predicts the dynamical variation of the focal distance, in good agreement with experiments. This effect plays a major role in the determination of the effective duration of the energy pulse. The model was used to conduct simple calculations of energy thresholds for melting of solid materials, giving helpful insight on ranges of operation of this kind of electron gun for its application to material processing. A comparison with available experimental data for Mg 70 Zn 30 samples is given.