Dye-enhanced nonlinearity threshold measurements in liquid crystals

• Autorzy: Sierakowski, M. , Waga, Ł.
• Konferencja: International Workshop on Nonlinear Optics Applications ; (7 ; 17-20.06.2004 ; Konstancin, Poland)
• Języki publikacji: EN

Abstrakty

EN

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).

Słowa kluczowe

EN

optical nonlinearity; liquid crystals; Janossy effect

• Czasopismo: Opto-Electronics Review
• Rocznik: 2005
• Tom: Vol. 13, No. 2
• Strony: 151-155
• Opis fizyczny: Bibliogr. 15 poz., il., wykr.

Twórcy

autor

Sierakowski, M.

• Faculty of Physics, Warsaw University of Technology, 75 Koszykowa Str., 00-662 Warsaw, Poland,

autor

Waga, Ł.

• Faculty of Physics, Warsaw University of Technology, 75 Koszykowa Str., 00-662 Warsaw, Poland

Bibliografia

• 1. M. Sierakowski, “Nonlinear liquid-crystalline optical cells”, Optica Appl. 24, 219-224 (1994).
• 2. I.C. Khoo and S.T. Woo, in Optics and Nonlinear Optics of Liquid Crystals, Series in nonlinear optics - Vol. 1, World Scientific Publishing, 1993.
• 3. C.M. Arakelyan and Yu.C. Tchilingaryan, Nieliniennya Optika Zhidkich Kristallov, Nauka, Moskva. (in Russian).
• 4. L. Marrucci, “Mechanism of giant optical nonlinearity in light absorbing liquid crystals”, Liquid Crystals Today 11, 6-33 (2002).
• 5. Even if the concentration of the dyes is a little different, the differences do not have to be concerned because in our experiment we noticed week sensitivity of the observed effect to the dye concentration in the examined range.
• 6. It should also result in reduction of the threshold of electro-optical Frederiks transition.
• 7. The analogical action of the chiral additives on molecular structure takes place by the forming of the cholesteric structure from the nematic phase.
• 8. I. Jánossy, “Molecular interpretation of the absorption-induced optical reorientation of nematic liquid crystals”, Phys. Rev. E49, 2957-2963 (1994).
• 9. I. Janossy and A.D. Lloyd, “Low power reorientation in dyed nematics”, Mol. Cryst. Liq. Cryst. 203, 77-84 (1991).
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• 12. L. Marrucci, D. Paparo, P. Maddalena, E. Prudnikova, and E. Santamato, “Role of guest-host intermolecular forces in photoinduced reorientation of dyed liquid crystals”, J. Chem. Phys. 107, 9783-9793 (1997).
• 13. E. Benkler, I. Janossy, and M. Kreutzer, “Control of the orientational nonlinearity through photoisomerization in dye doped nematics”, Mol. Cryst. Liq. Cryst. 375, 701-711 (2002).
• 14. M.I. Barnik, S.A. Kharchenko, V.F. Kitaeva, and A.S. Zolotko, “Reorientation of director of nematic liquid crystals doped with azodyes under light and low-frequency fields”, Mol. Cryst. Liq. Cryst. 375, 363-372 (2002).
• 15. T. Kosa, P. Palffy-Muhoray, H. Zhang, and T. Ikeda, “Large optical torque enhancement by oligothiophene dye in a nematic liquid crystal host”, Mol. Cryst. Liq. Cryst. 411, 107-131 (2004).