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A DISCUSSION of SOURCES of ERROR in LASER-SPECKLE BASED SYSTEMS

机译：基于激光斑点的系统中的错误源的讨论

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Applying laser-speckle techniques in the material sciences as well as in methods to characterize surface conditions of specimen has become the method of choice especially if a non-contacting principle is sought. This is almost always the case for specimen that are small in at least one dimension as for example in the material testing of foils, fibres or micromaterials and certainly also if elevated test-temperatures are preventing standard gauges.In this paper some widely overlooked sources of errors that - if unavoidable - increase measurement uncertainty beyond the theoretical limit attainable are discussed and the magnitude of their influence is detailed. In particular the following effects are considered: The laser-source wavelength stability as well as its pointing stability, the effects caused by so-called schlieren occuring along the optical path as well as temperature effects causing changes in the systems geometry, thermally influencing the optical parameters of the imaging optics as well as the often overlooked and in most illumination systems unknown radius of curvature of the laser wavefronts used to illuminate the specimen.Small though as these influences seem, they might contribute significant uncertainties especially in material testing applications where the strain ε =Δℓ/ℓ is to be determined out of consecutive measurements of usually small changes in overall length ℓ of the specimens geometry parameter. Typical values of ε are bounded by ±2000 ppm (the typical range of Hooke's law for steel). So values of Δℓ on the order of tenth of micrometers for typical gauge lenghts around 50 mm yield ppm resolutions for e. Analyzing the above mentioned error sources one can quickly see that all of them, if not taken care of appropriately, carry the potential to cause significantly larger deviations than the resolution sought after demands.
机译：在材料科学以及表征样品表面状况的方法中应用激光散斑技术已成为一种选择方法，特别是在寻求非接触原理的情况下。对于至少一维尺寸较小的样品来说几乎总是这种情况，例如在箔，纤维或微材料的材料测试中，如果测试温度升高阻碍了标准量规的确定，当然也是如此。讨论了一些误差（如果不可避免）会增加测量不确定度，使其超出理论上可达到的极限，并详细说明了其影响程度。尤其要考虑以下影响：激光源的波长稳定性及其指向稳定性，由沿光路发生的所谓的席利伦效应引起的效应，以及引起系统几何形状变化的温度效应，会对光学产生热影响。成像光学系统的参数以及经常被忽略的照明系统以及在大多数照明系统中用于照亮标本的激光波前的曲率半径未知，尽管这些影响似乎很小，但它们可能会带来很大的不确定性，尤其是在材料测试应用中，应变ε=Δℓ/ℓ的确定应从试样几何参数总长度usually的通常很小变化的连续测量中确定。 ε的典型值以±2000 ppm为界（钢铁的胡克定律的典型范围）。因此，对于50 mm左右的典型标距长度，Δℓ的值约为十分之一微米，可产生e的ppm分辨率。通过分析上述错误源，可以很快地发现，如果没有适当注意的话，所有这些错误源都有可能引起比寻求解决方案大得多的偏差。

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