Synthesis and characterisation of azomethine class thermotropic liquid crystals and their application in nonlinear optics

Abstract

Liquid crystals of azomethine derivatives were synthesised and their molecular structures were confirmed by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. Mesomorphic studies using differential scanning calorimetry, X-ray diffraction and polarising optical microscope revealed that all of these compounds exhibit thermotropic mesophases over a temperature range. The nonlinear optical properties of these liquid crystals were studied using a Z-scan technique with 7 ns pulse duration at 532 nm. The nonlinear refractive index, and the third order nonlinear susceptibility, were measured to be of the order of and respectively. Reverse saturable absorption was identified as the main mechanism responsible for optical limiting.

Keywords:

• thermotropic liquid crystals
• nonlinear absorption
• Z-scan
• optical limiting

Acknowledgement

We thank Mr K.N. Sharafudeen and Mr P. Sudheesh of the Laser and Nonlinear Optics Laboratory, NIT Calicut, India, for their useful help in carrying out NLO experiments.