Abstract
Angle measurements at the uncertainty level of tens of nanoradian are needed in many applications, from precision mechanical industry to astronomy, geodesy and experimental physics. Nowadays state of the art instruments to measure large angles, i.e. angular encoders, can achieve resolutions to the nanoradian level, but the traceability to the angle unit is not guaranteed at the same level of uncertainty. A novel ring laser gyroscope has been designed and built in a joint research project between INRIM and INFN. The device is based on a gyroscope 50 cm in side-length mounted on a precision rotating table. Exploiting the Sagnac effect, it will behave as an ideal angular encoder capable of generating and measuring angles over the full circle interval with a target accuracy of the order of 10 nrad.
Highlights
High accuracy angle measurements are required in many applications ranging from precision engineering to astronomical telescope or experimental physics
The accuracy of angular encoders (AEs) is limited by two main effects: an uneven division of the circle in equal parts and the interpolation errors, mainly due to the optical reading system that subdivide the interval between two grating lines
These errors can amount to few microradian for high end encoders, in case of applications where high accuracy are needed, any angular encoder has to be calibrated with respect to a better quality angle standard, such as the state of the art angle standards maintained in the National Metrological Institutes (NMIs) [1,2,3,4]
Summary
High accuracy angle measurements are required in many applications ranging from precision engineering to astronomical telescope or experimental physics. Nowadays resolutions at the nanoradian level can be achieved by commercial instruments such as autocollimators (ACs) and angular encoders (AEs) The latter are based on the division of the circle in equal parts and are generally used to implement angle standards, since they can generate and measure large angles. Two laser beams counter-propagate in a ring cavity: when the RLG is rotated, the two beams experience a differential length of the effective optical path. This produces a relative frequency shift (Sagnac frequency) between the two oppositely travelling beams, which is proportional to the angular speed, according to equation (1).
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