Figure 1
Illustration: Alan Stonebraker

Figure 1: Experimental configuration used by Dixon et al. for measurement of femtoradian angular displacements. A laser beam enters a Sagnac interferometer through an optical fiber and the output is monitored for amplitude changes by a CCD camera and for deflections by a quadrant detector. The changes to be measured are produced by motions induced in one of the mirrors by a piezoelectric actuator. Other elements in the optical path are a half-wave plate (HWP), a Soleil-Babinet compensator (SBC), and a polarizing beamsplitter (BS). (Adapted from P. B. Dixon et al. [2])