Single beam interferometric angle measurement

We present an application of a quadrature phase interferometer to the measurement of the angular position of a parallel laser beam with interferometric precision. In our experimental realization we reach a resolution of 6.8 × 10−10 rad (1.4 × 10−4″) for 1 kHz bandwidth in a 2 × 10−2 rad (1°) range. This alternative to the optical lever technique features absolute calibration, independence of the sensitivity on the thermal drifts, and wide range of measurement at full accuracy.