Dual-arm Z-scan technique to extract dilute solute nonlinearities from solution measurements

Abstract

We present a technique in which small solute nonlinearities may be extracted from large solvent signals by performing simultaneous Z-scans on two samples (solvent and solution). By using a dual-arm Z-scan apparatus with identical arms, fitting error in determining the solute nonlinearity is reduced because the irradiance fluctuations are correlated for both the solvent and solution measurements. To verify the sensitivity of this technique, the dispersion of nonlinear refraction of a squaraine molecule is measured. Utilizing this technique allows for the effects of the solvent n(2) to be effectively eliminated, thus overcoming a longstanding problem in nonlinear optical characterization of organic dyes.