基于多色散斑延长效应的表面粗糙度测量及影响因素分析

Analysis of Affecting Factors on Surface Roughness Measurement Based on Polychromatic Speckle Elongation

粗糙表面在多波长激光束照射下形成的多色散斑场显示出散斑延长效应,利用此效应可以测量表面粗糙度,并且测量结果在一定条件下不受粗糙表面横向特征的影响。通过模拟计算随机粗糙表面的多色散斑场,以空间平均的多色散斑场局部自相关函数研究了平均散斑延长率〈χ〉对表面轮廓均方根偏差σh的依赖关系,分析了测量系统因素,如入射激光波长组合、成像器件光敏单元尺寸和动态范围对测量结果的影响。结果表明,以空间平均的局部自相关函数代替集平均的散斑自相关函数描述多色散斑延长效应是有效的;为达到一定的粗糙度测量精度,应选择合适的入射激光波长组合和合适的成像器件光敏单元尺寸。

Speckle elongation phenomenon can be observed when rough surface is illuminated by a polychromatic laser beam. Based on this dependence the surface roughness can be determined, in which the influence of transverse characteristic of rough surface can be neglected when certain conditions are satisfied. Through numerical simulation of polychromatic speckle pattern of random rough surface, by application of the local autocorrelation function of polychromatic speckle pattern using spatial average, the dependence of average speckle elongation ratio 〈 X〉 on rootmean-square Oh of surface profile amplitude is studied, and the influences of experimental factors are investigated, such as the wavelength combination of laser beams, the cell size and the resolution depth of image acquisition device on measure result. The results show that describing the polychromatic speckle elongation effect by autocorrelation function using spatial average instead of ensemble average is effective, and to obtain enough precision of surface roughness measurement, appropriate wavelength combination of laser beams and appropriate cell size of image acquisition device should be chosen.