Measurement of the pretilt angle and the cell gap of nematic liquid crystal cells by heterodyne interferometry

Abstract

This work proposes a simple method, based on the crystal rotation technique and heterodyne interferometry, to simultaneously determine the pretilt angle and cell gap of nematic liquid crystal cells. When heterodyne light passes through a nematic liquid crystal cell, the phase retardation given by the characteristic parameters of the cell can be measured accurately by heterodyne interferometry. This phase retardation relates to the pretilt angle, cell gap, and angle of incidence on the cell. By using the measured phase retardations at two incident angles, the pretilt angle and cell gap of the nematic liquid crystal cell can be estimated by numerical analysis. This method is feasible, requiring only two incident angles and prior knowledge of two characteristic parameters--extraordinary and ordinary refractive indices of the liquid crystal. It is characterized by the advantages of simplicity of installation, ease of operation, high stability, high accuracy, and high resolution.

Polyhedral Oligomeric Silsesquioxane Films for Liquid Crystal Alignment

“…The voltage-dependent optical transmittance of LC cells placed between crossed polarizers was measured using a diode laser (~635 nm), and the applied voltage was a 1 kHz square wave. The pretilt angles of the LC cells were measured by the modified crystal rotation method [19], and the polar anchoring energy of the POSS alignment films was measured by using the high electric field method [20], where a heterodyne interferometer was used to determine phase retardation [21].…”

A Birefringent-Refraction Transducer for Measuring Angular Displacement Based on Heterodyne Interferometry

“…Phase measurements based on angle scanning methods have been proposed to measure the retardation parameters of the multiple-order wave plate [14], and the liquid crystal cell parameters (pretilt angle and the cell gap) [15]. The results of studies measuring retardation parameters show that phase delay is deeply dependent on crystal orientations [14].…”

Inline Quality Control of Liquid Crystal Cells

“…Besides the birefringence and orientation of the LC director, the change of the light polarization depends on the thickness of the LC layer. This fact is used in the majority of the techniques for filled LC cells [1][2][3][4][5][6][7][8][9][10][11][12][13][14][17][18][19]. However, determination of the state of polarization of the measured light often requires mechanical rotation or movement of either some polarization components of an experimental arrangement or an LC cell to be tested.…”

“…In monochromatic measurements, dependence of the light intensity on the incident angle is analyzed. Despite the variety of the proposed measuring techniques [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], only a few of them can be utilized for non-stop inspection of the quality control in a production line. Moreover, the majority of the developed methods are suitable for determination of a cell gap at no more than one point.…”