Research On Surface Roughness Measurement Method Based On Optical Interferometry

The function of the workpieee is highly influenced by its surface roughness. Tranditional stylus surface roughness measurement has a sensitivity of 0.1 nm and high transverse resolution, but it is easy to scratch the workpieee surface because of the contact between the stylus and the surface. But optical methods of surface roughness measurement can avoid this disadvantage and can reach a longitudinal sensitivity of 1 nm or even higher. Usually used optical measuring methods include: optical inteferemetric method, optical scattering method, optical stylus method and etc.Basic knowledge of surface roughness and traditional stylus surface roughness measuring method are simply introduced. Already reported surface roughness measurement method based on optics is detailedly introduced. A novel surface roughness measurement based on polarization inteferometry is proposed. A half and a quarter wave-plates are used to change the polarization states of the light beams, which makes the utmost of the inteferometric signals. Therotical analysis is given using Polarized optics and Jones Matrix theory. The measurement uncertainty induced by the limited resolution of the optical power meters is analysed. A surface roughness gauge block is measured using a frequency- and power-stabilized He-Ne laser and two LM-5E-typed optical power meters. The results show that the method is feasible, and the main source of the uncertainty is induced by the limited resolution of the power meters used.The method proposed here provides a reference to surface roughness measuement of inteferometric method.