Achievement of $\lambda$/4000 phase distortion sensitivity in the measurement of optical nonlinearities by using a modulated Z-scan technique

Abstract

We report on a modulation detection system that efficiently improves the signal-to-noise ratio and the maximum achievable sensitivity of Z-scan measurements of purely optical nonlinearities. By using suitable signal processing electronics and combining an averaging procedure with the harmonic motion of the sample around the Z-scan lens focus position, we demonstrate an increase of the measurement sensitivity of more than one order of magnitude, which is in principle independent of the particular Z-scan set-up employed. The consequence is that nonlinear phase distortions of λ/4000 can be easily measured and improvements up to λ/105 are foreseen.