Suppression of laser speckle contrast using negative dielectric anisotropy nematic liquid crystal doped with an ionic medium

Abstract

ABSTRACT A liquid crystal (LC) with negative dielectric anisotropy called N-(4-Methoxybenzylidene)-4-Butylaniline (MBBA) doped with the ionic agent cetyltrimethylammonium bromide (CTAB) has been investigated as a speckle suppression device to reduce the laser’s speckle contrast. The electrohydrodynamic instabilities (EHDI) effect in LC is exploited to reduce speckle contrast. The EHDI effect causes chaotic turbulence in LC, resulting in dynamic scattering of the incident light beam. In order to investigate the electro-optic properties and frequency region for optimal performance, optical measurements and dielectric spectroscopy of the pristine and doped LC are performed. The dielectric characteristics of the LC demonstrate that the frequency range to produce the EHDI effect in the LC cell is broadened as the ionic agent is doped. The inclusion of ions also enhances the ion density, mobility, and conductivity in LC. The increase in ion density and mobility enhances the turbulence in the LC at a faster rate; as a result, the dynamic scattering becomes more rapid. When measured with a charge-coupled device (CCD) camera, the faster dynamic scattering provides higher suppression in the laser’s speckle contrast. This method can be used to reduce the speckle contrast in laser source-based imaging and projection displays.