Generating and measuring pico-radian angles

Abstract

The angular performance of a nano-angle generator (NANGO) developed at Diamond Light Source has been characterised using a dual-beam laser interferometer designed and built at the National Physical Laboratory (NPL). NANGO is a flexure-based, piezo actuated device which generates milli- to sub-nano-radian angles for the calibration of metrology instruments used to test the quality of synchrotron X-ray mirrors and angular nano-positioning stages at Diamond. The NPL interferometer provides traceability for small angle measurements made by NANGO. An uncertainty budget has been developed for measurements over a 50 nanoradian range. In closed-loop, using feedback from the NANGO’s angle encoder, for the first time we show that 1 nanoradian steps made by NANGO are measurable by an external metrology device. The 200 kHz acquisition rate of the NPL angle interferometer also reveals new dynamic information about NANGO’s angular motion. The NPL interferometer demonstrates that NANGO in open-loop can make: distinct steps of 500 picoradians; sinusoidal oscillations at 0.4 Hz with an amplitude of 125 picoradians; or 1 nanoradian oscillations at 40 Hz. Traceability to the SI though National Metrology Institute instrumentation for NANGO will provide enhanced accuracy for a wide range of angle metrology applications at Diamond, including inputs to deterministic polishing techniques for the creation of next-generation X-ray mirrors and dynamic characterisation of nano-positioning stages.

D6.2 - Measuring sub nanoradian angles

“…Through this work, we have identified areas for improvement both in NANGO and the interferometer. Further details of this work together with an uncertainty budget can be found [6].…”

“…IOP publishing are thanked for permission to reproduce figures from [6] and the Department for Business Energy and Industry Strategy UK is thanked for funding.…”

Editorial for the Metrologia Focus Issue on Length Metrology

“…Length metrology plays an important role in providing traceability for high profile science activities and this is shown in a paper where precision angle metrology is being provided as an enabling input to such experiments [16].…”

“…The field of angle metrology, which is associated with length metrology, is also pushing the boundaries of achievable resolution as demonstrated by traceable measurement of angles with sub-nanoradian resolution [16] whilst still continuing to deliver high accuracy calibration of angle devices [20]. The need to deliver NMI-level angle metrology in an industrial/research setting was foreseen in the 2018 CCL Strategy Document [21] which saw the need to realise the SI units in situ, where the highest accuracies are required.…”