On the determination of order parameters for homogeneous and twisted nematic liquid crystals from Raman spectroscopy

Traditional approaches to the use of Raman spectroscopy as an aid to the determination of local order parameters in liquid crystalline materials have employed polarizations of the excitation source and/or the analyser which are orthogonal to the liquid crystalline director. The present paper describes a Raman study, which seeks to take advantage of the additional information available from examining the complete range of orientations of the director in relation to these polarization directions. A theory is developed which shows how it is possible to use this additional information to derive more reliable values of the P₂ and P₄ local order parameters in homogeneous and twisted nematic liquid crystal cells.