Comparison of Conventional Light Scattering and Speckle Techniques Concerning an In-Process Characterisation of Engineered Surfaces

Abstract

It is well known that several features of engineered surfaces can be determined by light scattering techniques. However, the characterisation of surface microtopography by scattered light sometimes only yields a qualitative assessment or does not directly correspond to common roughness parameters. The latter shortcoming may even lead to ambiguity, so that these techniques are hardly accepted for industrial quality inspection. Nevertheless, the technological progress in the field of optoelectronics (laser diodes, CCD- and CMOS-cameras, digital image processing) allows a compact realisation of novel arrangements. In this contribution, light scattering and speckle techniques for a measuring range from 1 nm to about 10 μm (rms-roughness) will be introduced. Conventional light scattering methods relevant to industrial applications are known as “angle resolved scattering” (ARS) and diffuseness measurement. The speckle techniques include the method of polychromatic speckle autocorrelation and the doubly scattered light approach, which have been recently developed by the authors. The different parametric methods will be compared with respect to their in-process capabilities and the correlation between optical output parameters and statistical parameters of the surface profile under investigation. Furthermore, it will be shown that 3D-quantities of engineered surfaces can be obtained from the measuring data.