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The laser flash analysis or laser flash method is used to measure thermal diffusivity of a multiplicity of different materials. An energy pulse heats one side of a plane-parallel sample. The temperature rise on the backside due to the energy input is time-dependent detected. The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. A state-of-the-art laser flash apparatus (LFA) to measure thermal diffusivity over a broad temperature range, is shown on the right hand side. In a one-dimensional, adiabatic case the thermal diffusivity is calculated from this temperature rise as follows: : is the time to the half maximum ==Measurement principle== The laser flash method was developed by Parker et al. in 1961.〔 〕 In a vertical setup a light source (e.g. laser, flashlamp) heats the sample from the bottom side and a detector on top detects the time-dependent temperature rise. For measuring the thermal diffusivity, which is strongly temperature-dependent, at different temperatures the sample can be placed in a furnace at constant temperature. Perfect conditions are * homogenous material, * a homogenous energy input on the front side * a time-dependent short pulse - in form of a Dirac delta function Several improvements on the models have been made. In 1963 Cowan takes radiation and convection on the surface into account.〔 〕 Cape and Lehman consider transient heat transfer, finite pulse effects and also heat losses in the same year.〔 〕 Blumm and Opfermann improved the Cape-Lehman-Model with high order solutions of radial transient heat transfer and facial heat loss, non-linear regression routine in case of high heat losses and an advanced, patented pulse length correction.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Laser flash analysis」の詳細全文を読む スポンサード リンク
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