Enhancement of the nonlinear optical absorption of the E7 liquid crystal at the nematic-isotropic transition

TL;DR

This study investigates how the nonlinear optical absorption of E7 liquid crystal changes at the nematic-isotropic phase transition using Z-scan technique, revealing phase-dependent nonlinear coefficients and critical behavior consistent with a tri-critical transition.

Contribution

It provides experimental evidence of phase-dependent nonlinear optical coefficients and their critical behavior at the nematic-isotropic transition in E7 liquid crystal.

Findings

Nonlinear optical coefficient eta is negative for extraordinary and positive for ordinary beams in the nematic phase.

The nonlinear absorption parameter S_{NL} behaves like an order parameter with a critical exponent of 0.22.

The behavior supports the tri-critical hypothesis of the nematic-isotropic phase transition.

Abstract

We present an experimental study of the nonlinear optical absorption of the eutectic mixture E7 at the nematic-isotropic phase transition by the Z-scan technique, under a continuos wave excitation at 532 nm. In the nematic region, the effective nonlinear optical coefficient \beta for an extraordinary beam is negative and for an ordinary beam is positive, being null in the isotropic phase. The parameter S_{NL} defined in terms of the nonlinear absorption coefficients in a similar way than the optical order parameter from the linear dichoic ratio behavies like an order parameter with a critical exponent 0.22+-0.05, in good agreement with the tri-critical hipothesis of the N-I transition.