Nonlinear optical properties of liquid crystals probed by Z-scan technique

Abstract

We present a review of experimental data on the nonlinear optical properties of thermotropic and lyotropic liquid crystals probed by the Z-scan technique. Depending on the time scale, different processes originate a nonlinear optical response. Particularly, at nanosecond range, the physical processes associated with the nonlinear response in thermotropics are not completely understood. In lyotropics, the nonlinear response at ms time scale is from thermal origin and depends on the particular mesophase, relative concentration of the components, and temperature.

Z-scan and optical limiting properties of Hibiscus Sabdariffa dye

“…Accordingly, one could then generalize the remark by Henari et al on the large value of n 2 of the Hibiscus Sabdariffa dye solutions that they have investigated for a fixed concentration (The concentration by weight of their sample solution was 2.02 9 10 -2 ). The current n 2 values are all larger by one order of magnitude than the value reported for the Chinese tea and thermotropic liquid crystals [19,20], and much larger, indeed than that of the reported values for photorefractive crystals, liquid crystals and fullerenes [21,22]. Both the n 2 and Realv (3) values obtained are equivalent to those of Rekha and Ramalingam obtained on Carmine (C 22 H 20 O 13 ) and Safranin O (C 20-H 19 N 4 Cl) natural dye solutions with a similar, yet a CW Nd:YAG laser source emitting at 532 nm [2,23].…”

“…The nonlinear optical properties, in addition to the optical limiting, were investigated by z-scan technique, which has the advantages of simplicity and high sensitivity, as well as enabling simultaneous measurement of the magnitude and sign of the nonlinear refractive index and the nonlinear absorption coefficient of the samples [16][17][18][19][20][21][22][23][24][25][26][27]. Basically, the method consists of translating a sample through the focus of a Gaussian beam and monitoring the changes in the far field intensity pattern (Fig.…”

Effect of polymer host on third order nonlinear optical properties of newly synthesized organic liquid crystal

“…Thus the nonlinear optical response is mainly due to the π-electrons of the benzene rings. The negative nonlinear refraction is due to the change in the density of the medium, which overcomes the positive sign of the transient orientational nonlinearity [8]. The magnitude of third order nonlinear parameters increases when the compound is doped into PMMA matrix because of the change in the conformation of chain geometry as a result of charge transfer processes.…”

Crystal Structure and Third Order Nonlinear Optical Studies on 2-Phenylbenzimidazolium-P-Toulenesulphonate

“…The real and imaginary parts of the third order nonlinear susceptibility χ(3) are defined as where k is the wave number k = 2p/λ and where ε 0 is the vacuum permittivity, n 0 is the linear refractive index of the sample and c is the velocity of light in vacuum. Thus, we can easily obtain the absolute value of χ(3) using the following formula As seen from the closed aperture Z scan curve, the prefocal transmittance valley is followed by the post focal peak, which is the positive nonlinearity 15 . The calculated value of the nonlinear refractive index (n 2 ) is 6.40149 10 -8 cm 2 /W.…”