DOI: 10.1007/s101890070037
Optical studies in liquid crystals using the high-accuracy universal polarimeter
J. Ortega1, J. Etxebarria2 and C.L. Folcia21 Departamento de Física Aplicada II, Facultad de Ciencias, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
2 Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain
wmporapj@lg.ehu.es
wmpetecj@lg.ehu.es
(Received 13 September 1999 and Received in final form 25 January 2000)
Abstract
The so-called high-accuracy universal polarimeter
(HAUP) is introduced as a tool to study optical properties of
liquid crystals. It is shown that besides homogeneous crystals, the
HAUP method also permits to investigate inhomogeneous materials,
provided that the optical parameters vary slowly on a wavelength
scale. The technique is especially useful when small effects are
sought. Measurements are presented for several twisted nematic
samples. Twist angles are measured with high accuracy and
non-adiabatic effects for light propagation, such as apparent
indicatrix rotations or effective gyrations, are easily detected.
The results agree well with the predictions of a first-order
perturbation treatment for light propagation through a stratified
medium. Finally, the changes of the director profile are analyzed
in a planar sample that presents a chiral nematic to smectic-A
transition. The experimental data indicate that if the rubbing
directions of the cell are not strictly parallel, the molecules at
the surfaces undergo small twists in both phases, and the twist
parameters are determined.
61.30.-v - Liquid crystals.
78.20.-e - Optical properties of bulk materials and thin films.
64.70.Md - Transitions in liquid crystals.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2000
