Development of a System for Measuring Thermal Diffusivity of Thin Films by Laser Flash Method Based on a New Principle.

本文提出了一种平行于或垂直于薄膜样品表面方向的热扩散率激光测量方法。在测量样品平行方向时，将具有窄线形截面的脉冲激光束照射到样品的前表面。利用红外探测器测量距离激光束线状照射区域一定距离处的后表面温度响应，通过实测温度响应曲线与理论温度响应曲线的比较，可以确定热扩散系数值。另一方面，在垂直于薄膜样品表面方向上的热扩散率测量，将直径约为10 mm的脉冲激光束照射到样品的前表面。后表面的温度响应由红外探测器测量。热扩散系数值可以通过与包括脉冲持续时间在内的理论解进行比较来确定。通过对铂（25 μ m）、铜（18 μ m）、SUS304不锈钢（50 μ m）和镍（130 μ m）等金属箔样品的热扩散系数的测量，证明了该方法的有效性。激光闪光法测量各种无机物的热扩散系数通常采用红宝石激光器，由于其能量分布的不均匀性及其特殊的空间强度结构，在某些情况下会严重影响所得热扩散系数数据的定量准确性。为了使激光束在试样表面的能量分布均匀化，提出了一种由塑料光纤和塑料光导杆组成的随机光纤束。通过测量镍片的能量分布和热扩散系数，证明了该装置的实用性。提出了一种用激光闪光法测量液体样品在高温下的热扩散率的简单单元和易于处理的数据。电池由夹在两个金属板中间的液体样品组成。将一块金属板的前表面暴露在单脉冲激光束下，测量另一块金属板后表面的温升。为了估计液体样品的热扩散系数值，将James提出的利用两层细胞体系温度响应曲线初始时间区域的对数分析方法推广到目前的三层细胞体系。首先对蒸馏水和甲醇进行了测量，结果与参考数据吻合良好。然后，测定了593 ~ 660 K和621 ~ 694 K下的NaNO_3和KNO_3熔液的热扩散系数，结果与文献报道的结果吻合较好。少

A laser flash method for measuring thermal diffusivity in the direction parallel or perpendicular to the sample surface of film has been developed. On measurement of parallel direction of a sample, a pulsed laser beam which has narrow line-shaped cross section is flashed onto the front surface of the sample. The temperature response at the back surface at a certain distance away fro the line-shaped illuminated area of a laser beam is measured by the infrared detector and the thermal diffusivity value can be dete mined by comparing measured temperature response curve with theoretical one. On the other hand, the measurement of thermal diffusivity in the direction perpendicular to the sample surface of a film, a pulsed laser beam whose diameter is about 10 mm, is flashed onto the front surface of the sample. The temperature response at the back surface is measured by the infrared detector. The thermal diffusivity value can be determined by comparing with the theoretical solution including … More a pulse duration. The usefulness the present method has been demonstrated by measuring successfully thermal diffusivities of metallic foil samples of platinum (25 mum copper (18 mum), SUS304 stainles s steel (50 mum) and nickel (130 mum).Ruby lasers usually employed in the laser flash method for measuring thermal diffusivity of various inorganic substances a known to have the inhomogeneous energy distribution and their particular spatial intensity structure significantly effects the quantitative accuracy of the resultant thermal diffusivity data in some cases. Random packed fiber bundle made of plastic optical fiber wi plastic optical guiding rod has been developed for homogenizing the energy distribution in a laser beam on the specimen surface. T usefulness of this new device has been well approved by measuring the energy distribution and the thermal diffusivity of nickel disc.A simple cell and easy data processing have been proposed for measuring the thermal diffusivity of a liquid sample at high temperatures using the laser flash method. A cell consists of a liquid sample sandwiched by two metallic plates. The front surface one metallic plate is exposed to a single pulse of beam laser and the resulting temperature rise of the back surface of the other metal plate is measured. The logarithmic analysis proposed by James using the initial time region of the temperature response curve of a two layered cell system has been extended to apply to the present three layered cell system in order to estimate the thermal diffusivity value of a liquid sample. Measurements of distilled water and methanol were made first and the results were found to be in good agreement with the reference data. Then, the thermal diffusivities of molten NaNO_3 at 593-660 K and of molten KNO_3 at 621-694 were determined and the results also appear to agree reasonably well with those reported in the literature. Less