Abstract
Nanoradian Surface Profilers (NSPs) are required for state-of-the-art synchrotron radiation optics and high-precision optical measurements. Nano-radian accuracy must be maintained in the large-angle test range. However, the beams' notable lateral motions during tests of most operating profilers, combined with the insufficiencies of their optical components, generate significant errors of∼1 μrad rms in the measurements. The solution to nano-radian accuracy for the new generation of surface profilers in this range is to apply a scanning optical head, combined with nontilted reference beam. I describe here my comparison of different scan modes and discuss some test results.
Highlights
Construction started on ultrabright SR sources with nanofocusing spots at the National Synchrotron Light Source II (NSLS II), Brookhaven National Laboratory (BNL) in the United States and at the Taiwan Photon Source (TPS) of the NSSRC in Taiwan
During the stability scan of the Long Trace Profiler (LTP) MF (PBS, FT and DET on Figure 7), an external pencil beam is scanned laterally to simulate the Beam Lateral Motion (BLM) over the LTP MF aperture by a pentaprism
To reach nanoradian accuracy in the larger testing range for a surface profiler, the designer should consider eliminating or significantly reducing the beam’s lateral motion thereby to decrease the impact caused by the imperfect optical components sited in the optical system’s testing path
Summary
The traditional null interferometer can measure a 2D sphere or aspheric surface in full aperture with an accuracy of about λ/30. Required focusing spot size 10 μm 1 μm 1 nm aspheric surfaces normally have a short radius of curvature, of tens millimeters sagittally, and several hundred meters or much more meridianly They are hard to measure with a traditional null interferometer, a CGH or an SSI. The NOM combines, in a comparison test, an LTP and a commercial autocollimator with a small aperture Both instruments operate in a scanning pentaprism mode without a reference beam. A new traceable multiple sensor (TMS) system was developed recently for measuring with nanometer accuracy It encompasses coupled multiple distance-sensors that are scanned along the surface under test. Accuracy becomes problematic when they are used for testing largeslope surfaces
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