Approach to improve the angle sensitivity and resolution of the optical beam deflection method using a passive interferometer and a Ronchi grating

We discuss a new detection scheme to measure very small angular deflections of a Gaussian beam. We show that it is possible to increase the sensitivity to angular deflection substantially in comparison with the conventional optical beam deflection method (OBDM). It is shown that the theoretical limit to the minimum detectable angle when the detection is assumed to be shot-noise-limited may be improved ac- cordingly. A detailed analysis of the conventional OBDM for the purpose of comparison is also presented. A proof-of-principle experiment is de- scribed, and some experimental results are given.