Optical second harmonic generation in a ferromagnetic liquid crystal

TL;DR

This study compares second harmonic generation in standard and ferromagnetic nematic liquid crystals under various external stimuli, revealing the contributions of electric and magnetic fields to nonlinear optical responses.

Contribution

It provides the first detailed comparison of SHG dependence on electric and magnetic fields in ferromagnetic versus standard nematic liquid crystals.

Findings

SHG in ferromagnetic liquid crystals arises from EFISHG and flexoelectric effects.

SHG in standard nematic liquid crystals is mainly due to flexoelectric effects.

Both contributions can generate comparable nonlinear susceptibilities in optimal conditions.

Abstract

A comparative experimental investigation of the dependence of second harmonic generation (SHG) on applied external voltage between the standard nematic liquid crystalline material and an analogue ferromagnetic nematic liquid crystalline material was performed by using a fundamental optical beam at 800 nm wavelength. For a ferromagnetic material, the dependence of SHG on an applied magnetic field was also examined. Three different polarization combinations of the fundamental and the second harmonic radiation were analysed. The SHG signal observed in the former material is attributed to a combination of electric field-induced SHG (EFISHG) and flexoelectric deformation-induced SHG, while SHG signal observed in the latter material is attributed solely to flexoelectric deformation-induced SHG. The obtained dependences of the SHG signal on the associated optical retardation show that in the most favourable polarization combination the two contributions generate about the same effective nonlinear optical susceptibility.