Highly linear sub-nanoradian tilt measurement based on dual-beam interferometry

The tilt measurement method based on dual-beam interferometry is presented in this Letter. Due to symmetric property of the nonlinear errors of two displacement measurement arms, the composite nonlinearity of the tilt measurement is counterbalanced, so that a small nonlinearity over a large dynamic range can be obtained. According to the theoretical analysis with a Gaussian beam model, the second-order nonlinear error is dominant. The experimental results show that a measurement noise of 0.4nrad/Hz at 1 Hz with a nonlinearity of less than 60 nrad for a measurement range of ±500µrad has been achieved.