Articolo in rivista, 2007, ENG

Optical characterization of liquid crystals by combined ellipsometry and half-leaky-guided-mode spectroscopy in the visible-near infrared range

Abbate G., Tkachenko V., Marino A., Vita F., Giocondo M., Mazzulla A., De Stefano L.

Coherentia & LiCryl CNR INFM, I-80126 Naples, Italy; Univ Naples Federico II, Dept Phys Sci, I-80126 Naples, Italy; LiCryl CNR INFM, I-87036 Arcavacata Di Rende, Italy; Univ Calabria, CEMIF CAL, Dept Phys, I-87036 Cosenza, Italy; CNR IMM, I-80131 Naples, Italy Coherentia & LiCryl CNR INFM, I-80126 Naples, Italy; Univ Naples Federico II, Dept Phys Sci, I-80126 Naples, Italy; LiCryl CNR INFM, I-87036 Arcavacata Di Rende, Italy; Univ Calabria, CEMIF CAL, Dept Phys, I-87036 Cosenza, Italy; CNR-IMM, I-80131 Naples, Italy

In this paper, we present our results for the anisotropic refractive index measurements of commonly used liquid crystal (LC) materials (E7 and 5CB) in the whole visible-near infrared range. In order to achieve a high accuracy in the obtained values, we have employed a combination of two techniques, namely, Mueller matrix spectroscopic ellipsometry in transmission and half-leaky-guided-mode (HLGM). Measurements with the HLGM technique are usually performed at a single wavelength. In order to obtain a spectroscopic measurement based on the HLGM technique in a wide wavelength range, we modified our commercial VASE((R)) ellipsometer. In particular, we designed a sample holder by means of which measurements in guiding structures are also possible. Thus, we take advantage of the wide-spectrum light, emitted from a standard Xe lamp of the ellipsometer, also in the HLGM setup. The complementary and in-one-setup utilization of both techniques has allowed us to overcome most of the problems previously encountered in applying spectroscopic ellipsometry to the determination of the optical parameters of LC materials and eventually to achieve an accuracy in the obtained results of the order of 10(-4). We discuss how individual elements of the Mueller matrix can be used to this aim. Finally, we compare the dispersion curves for the refractive indices and the birefringence of E7 and 5CB with the data already existing in the literature. (c) 2007 American Institute of Physics.

Journal of applied physics 101 , pp. 73105–73105

Keywords

REFRACTIVE-INDEXES, THIN-FILMS, TEMPERATURE, MATRIX

CNR authors

Abbate Giancarlo, Marino Antigone, De Stefano Luca, Tkachenko Volodymyr, Mazzulla Alfredo, Giocondo Michele

CNR institutes

IMM – Istituto per la microelettronica e microsistemi, IPCF – Istituto per i processi chimico-fisici, INFM – Centro di responsabilità scientifica INFM