Advance in a nano-accuracy surface profiler with an extended-angle test range

An advanced design of a nano-accuracy surface profiler (NSP) is introduced wherein we combined a scanning optical head with non-tilted reference system to facilitate measurements over an extended range of angles. The lateral motion of the beam during testing of a strongly curved mirror induces a systematic error. For a pencil-beam scanning profiler, the arm with varying optical-path lengths should be non-tilted so to eliminate the beam's lateral motion, and the arm for testing larger angles should be short and fixed so to reduce the beam's lateral motion. Our new scheme of having a non-tilted reference system offers an effective, simple, and convenient solution. A beam spot of 0.5–1 mm is used for higher spatial frequency tests in surface-figure measurements. Some preliminary studies and test are demonstrated.