Testing a new method for small-angle rotation measurements with the optical vortex interferometer

We present an application of the optical vortex interferometer (OVI). The OVI is based on a regular net of optical vortices that are generated by the interference of three plane waves. If one of the interfering waves is distorted then the geometry of the vortices net is changed. The measurement is based on tracking the change in the vortices' position. One application of the OVI is to use it to determine small-angle rotation. The OVI distinguishes two axes of rotation and the corresponding two rotation angles can be measured with sub-arcsecond resolution. The linear vibrations of the measured element are automatically subtracted. A single measurement provides hundreds of measurement points, so statistical methods for data analysis and correction can be applied effectively. In this paper we present an experimental test of the method. To get a precise rotation of one of the interfering waves an optical wedge is put into one of the interferometer arms. The analysis shows that the decrease in amplitude does not influence the measurement accuracy. From the shifting of the vortex net the rotation angle of one of the interfering, waves is calculated and this rotation is used to calculate the refracting angle of the applied optical wedge.