Oblique light incidence method to study topological defects in nematic layers with conical boundary conditions

Abstract

AbstractA polarization microscopy method to investigate the orientational structures and boojums formed in the chiral and achiral nematic layers under conical (tilted) boundary conditions has been developed. Oblique light incidence on nematic layer is used, due to which the phase difference between the ordinary and extraordinary waves depends on the director’s azimuthal angle. The phase difference gets maximal when the director azimuthal angle of achiral nematic $$\varphi (x,y) = 0$$ φ ( x , y ) = 0 and an azimuthal angle at the center of the chiral nematic layer $$\varphi _0(x,y) = 0$$ φ 0 ( x , y ) = 0 independently of the total twist angle $$\varphi _{TOTAL}$$ φ TOTAL . It has been found that the $$m=+1$$ m = + 1 boojums with the phase $$\xi = \pm 90^\circ$$ ξ = ± 90 ∘ and $$\xi = (-90^\circ + \varphi _{TOTAL}/2)$$ ξ = ( - 90 ∘ + φ TOTAL / 2 ) are formed in achiral and chiral nematics, respectively, at the director tilt angle $$\theta _{d/2} \cong 40^\circ$$ θ d / 2 ≅ 40 ∘ at the interface. In addition, the defectless structure of chiral nematic with the periodically variable azimuthal director angle on the substrates has been studied.