A Novel Profilometer for Nanometric Form Assessment for Large Machined Surfaces

We report a new point-by-point stylus profilometer for efficient form assessment for large and curved optical surfaces. The system consists of a laser reference system and a low contact force type stylus system. For laser datum referencing, the freely propagated laser beam is monitored by a nulling quadrant photodiode mounted on a flexure system with hybrid actuators, which also carries interferometer reference optics for vertical displacement measurement. The compensation accuracy of the reference system is within 10 nm for the external disturbance of 0.7 μm. The stylus system adapts a hybrid type of plunger and pivot for the long travel length of approximately 30 mm and a low contact force of 70 mg. This probe system shows a repeatability of less than 10 nm for 10 for up to 8.1 degrees of slope. The performance of the reference and probe systems was measured. The results demonstrate its applicability for the form measurement of large and curved optical surfaces both ground and polished during the fabrication process.