4 D Metrology of grinded surfaces based on short coherent interferometry

In the manufacturing process of aspheric and free-form glass surfaces the high accuracy measurements of the grinded set plays a key role both in respect of the quality of the overall final achievable optical surface as well as in respect of manufacturing costs. Therefore, there is a need for the measurement device to monitor such important aspects as surface topography and SSD (subsurface damages) during and after grinding process. The typically used tactile measuring machines for measuring the grinded surface topography prove sufficient precision regarding depth resolution but suffer from limited lateral resolution, which is necessary to detect SSD. Especially, the nondestructive measurement of SSD is a challenge for the metrology of grinding surfaces. In order to detect SSD a three dimensional optical imaging technique with high dynamic range based on short coherent interferometry was set up and the first tests were made on calibrated gratings and grinded lens elements. The measurement results show, that the method is feasible to monitor the most relevant parameter for grinding