投影像の明暗解析によるガラスの表面うねり形状の測定

抄録

This paper proposes a method to measure surface profiles of flat glasses by using a shadow image generated by the surface corrugations. When a point light is projected to a screen through the glasses, surface corrugations work as lenses to modulate contrast on the screen. Peaks on the glass surface give brighter regions and valleys gives darker regions, so brightness profiles on the screen agree to surface profiles. Contrasts of shadow images are predicted by an optical theory and lens model of surface profiles. The predictions agree to experiments for various optical positioning and installation angle. High contrast profiles of shadow images do not always give high similarity to the surface profiles because of the blur for too strong lens effect and resolution limit. On an allowable condition, three samples are measured whose surface profiles have peak-to-valley corrugation of 10-65 nm. For each sample, both surface profiles and brightness profiles give similar waveforms. An error of 5 nm is defined from the difference between both profiles for a pitch of 1 mm. This simple method can be applied to measure the surface profiles of flat glass with high accuracy.