数字全息干涉相位导数计算的研究

应变测量对材料评估与分析非常重要。通过计算数字全息干涉的相位导数可实现应变测量。本文针对数字全息干涉相位导数提取问题,对数字剪切法和基于二维伪维格纳法进行研究。数字剪切法通过对干涉复相量的数字平移实现剪切,确定干涉相位导数,而二维伪维格纳法则通过对干涉复相量的二维伪维格纳分布变换,由变换模极值对应的频域参数确定相位导数。数字剪切法需干涉复相量的数字剪切过程,还需相位去包裹。由于激光散斑噪声的影响,直接数字剪切法处理效果较差,通过对剪切干涉复相量滤波,能较好消除散斑噪声影响。二维伪维格纳法无需数字剪切和相位去包裹,就可同时得到2个方向的干涉相位导数,但处理时间较长,处理效果较差。最后,用数字全息干涉法对四周固定、中心加载铝圆盘进行了实际测量,并分别用数字剪切法和二维伪维格纳法进行了分析。结果表明,滤波数字剪切法处理时间适中,处理效果较好。

Research on the Algorithm of Phase Derivative in Digital Holographic Interferometry

Strain measurement is very important to material evaluation and analysis. Strain measurement can be realized through calculation of phase derivative in digital holographic interferometry. Aiming at the extraction of phase derivative in digital holographic interferometry, digital shearing method and two-dimensional pseudo Wigner method were studied respectively. Digital shearing method realizes digit cut through digit translation of interferometry complex phasor to determine interferometric phase derivative. While two-dimensional pseudo Wigner method determines interferometric phase derivative through transforming frequency-domain parameters corresponding to modulus extremum based on two-dimensional pseudo Wigner distribution transform of interferometry complex phasor. Digital shearing method needs the digital shearing process of interferometry complex phasor and phase unwrapping. The effect of direct digital shearing is poor due to the influence of laser speckle noise. This shortcoming can be improved by filtering the sheared interference complex phasor. Two-dimensional pseudo Wigner method enables simultaneously estimate phase derivative of interferometric complex phasor along both horizontal and perpendicular directions without digital shearing and phase unwrapping. But its shortcomings are long processing time and poor effect. Finally, adopting a fully-clamped circular aluminum disk with central load as test specimen, actual measurement was carried out by digital holographic interferometry. Experimental results were analyzed by digital shearing method and two-dimensional pseudo Wigner method, respectively, Results show that digital shearing method with filtering processing presents better treatment effect and moderate processing time.