A cholesteric liquid crystal has mean refractive index and birefringence

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Condensed Matter, Materials & Soft Matter · Polarisation and anisotropic media

Soft Matter at the Thermal Scale, Ch Frank elasticity, defects and smectic layers

Problem

A cholesteric liquid crystal has mean refractive index

\bar n = 1.50

and birefringence

\Delta n = 0.15

. It reflects red light at the wavelength

\lambda_0 = 650\,\mathrm{nm}

. ((a)) Find the helical pitch

p

. ((b)) Find the width

\Delta\lambda

of the reflected band.