Event Date
A two-beam interferometer measures the difference of phases accumulated by two optical beams, - originated from a same source, that traverse two physical paths and meet again at some point in space. A Sagnac interferometer is a specially configured two-bean interferometer in which the two optical beams traverse a same physical path but in opposite directions and the path thus forms a loop, - a Sagnac loop. When the loop rotates with respect to an inertial frame and the projected area of the loop on the plane of rotation is none zero as Sagnac did in 1913, he observed a non-zero phase difference that is known as the Sagnac Effect. I will briefly explain how Special Relativity of Einstein explains the Sagnac Effect when suitable clocks are used. When a Sagnac loop encloses no area, time-reversal symmetry breaking effects in the optical elements in the Sagnac loop can still introduce extra measurable phases that have opposite signs for the two counter-propagating beams. I will describe how such a zero-area Sagnac interferometer in different configurations have been explored in my group in recent years for investigating magnetic materials and other time-reversal symmetry breaking effects in unconventional materials with symmetry-allowed high sensitivity.