Reducing Systematic Errors in Thermal Diffusivity Laser Flash Measurements Caused by Detector Inherent Delayed Response

Laser flash apparatuses (LFA) are a widely used method to determine thermal diffusivity. Different factors influencing the quality of the diffusivity determination have been identified. Especially for thin samples, detector related time delays between the triggering of a laser pulse and signal detection as well as the shape of the laser pulse may become crucial for precise measurements. It is well known how to detect and account for laser pulse shape with respect to the trigger signal (“finite pulse-time effect”). An additional delayed response of the signal can be caused by detectors and electronic components (e.g. electronic filters) and inherent to LFA measurements. To correct for this additional delay, the detector signal of direct laser pulses was measured and a transfer function derived. This allows to account for the laser-pulse-detector behavior, based on the measured characteristic of the laser for different detectors (indium antimonide (InSb) and MCT (HgCdTe) detectors). The effect of the detector response is detector specific. For the experimental setup used, systematic errors caused by this effect are in the same range than the often considered finite pulse-time effect. ... mehrTo consider the actual pulse shape including the detector-sided retardation effect, a data evaluation routine based on the principles of superposition is developed. It includes a transfer function to adapt the detector signal using the pulse shape measured by diode within the apparatus. With this, the finite pulse-time effect as well as the detector-sided retardation is considered and systematic errors are effectively reduced. To avoid experimental uncertainties and to separate curve shape influencing factors, synthetic temperature response data are used to determine the systematic errors for various thermal diffusivities and sample thicknesses. By not taking into account the additional detector inherent retardation systematic errors > 10 % may arise for both, high and low temperature detectors, indium antimonide (InSb) and MCT (HgCdTe), respectively.