High-sensitivity roll-angle interferometer.

A roll-angle interferometer with high sensitivity is presented in this Letter. Two sets of centrosymmetric beams are used to travel through the measurement and reference arms of the roll-angle interferometer, which contains two specific optical devices: wedge prism assembly and wedge mirror assembly. Changes of the optical path in the interferometric arms caused by roll are differential and converted into phase shift through a particular interferometer system. The interferometric beams are a completely common path for the adoption of the centrosymmetric measurement structure, and the cross talk of the straightness, yaw, and pitch errors is avoided. The dead path is minimized, so the stability and the accuracy of the measurement can be greatly enhanced. The experimental results fit well with the theoretical analysis, and a measurement resolution of sub-microradian is achieved experimentally.