Ultra-sensitive measurement of third-order optical nonlinearity via weak value amplification

An ultrasensitive third-order optical nonlinearity measurement was theoretically proposed and experimentally demonstrated based on an extended Sagnac interferometer using weak value amplification. The predictable nonlinear refractive index coefficient (n2) of a nonlinear optical sample (nematic liquid crystals) accorded with the experimental result, which confirmed the rationality and feasibility of the proposed method. The sensitivity of the proposed method was associated with the resolution of the spectrometer and the postselection angle. By choosing a currently available spectrometer, the minimum Kerr phase of about 7.5 × 10−7 rad could be measured. Moreover, low cost and convenient operation of this method might have potential application in third-order optical nonlinearity measurements.