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1 Opto-Electronics Review

1 2005

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Dye-enhanced nonlinearity threshold measurements in liquid crystals

Sierakowski M., Waga Ł.

Opto-Electronics Review

2005

Vol. 13, No. 2

151-155

Since early eighties it is well known, that optical field can interact with liquid crystalline structures inducing molecular motion in similar way to quasi-electrostatic fields. This nonlinear optical effect (NOE) causes changes of refractive index distribution in the structure and in this way leads to several optical phenomena, like self-diffraction of the propagating beam, harmonic generation, four-wave mixing, nonlinear wave-guiding, etc. At first, NOE was observed in nematics for relatively high optical power densities. In the middle of nineties, Istvan Janossy discovered, that small addition of specific dopants to LC-material can significantly reduce the light power required for NOE. At present, NOE can be induced in certain LC-materials by sub-miliwatt laser beams. This achievement opened a way to many applications of the accompanied optical phenomena. Mechanism of the Janossy effect is still not quite clear. NOE is generally a threshold effect, which means that it starts after a certain threshold value of the optical power. In this work we examine the threshold of the self-diffraction of light in doped nematics in selected conditions, trying to understand its nature. Final goal of the work is examination of NOE in chiral liquidcrystal structures (cholesterics).