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Q: Quantenoptik
Q 10: Poster: Nonlinear Optics
Q 10.14: Poster
Dienstag, 3. April 2001, 12:30–15:00, AT2
Stduy of ferroelectric phases of bent-shaped molecules for SHG and applications for QPM waveguides — •Omar Morales-Saavedra1, F. Kentischer1, H.J. Eichler1, G. Priebe1, and R. Macdonald2 — 1Optisches Institut, TU Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany. — 2Physikalisch Technische Bundesanstalt Berlin, Abbestraße 5, 10623 Berlin, Germany.
We investigated new No-dqspiralingNo-dq so called B7-phases of banana-shaped liquid crystalline molecules with SHG-technique for the first time. Similar to the well known SmC-like B2-phase, the B7-phase can be switched by comparatively weak applied external electric fields, e.g. 3V/µm. High nonlinear coefficients have been observed in the electric field induced ferroelecetric state of the B7-phase The electric field dependence of the SH-signal exhibits a double hysteresis loop, which differ from those observed with the previously studied antiferroelectric B2 phase[1]: close to the saturation electric field strength the curves for increasing and decreasing electric field intersect.
Beside huge fundamental importance, such antiferroelectric NLO-active organic noncrystalline materials are interesting for the development of nonlinear optical devices such as NLO-waveguides for frequency conversion or fast e.-o.-switching (via the Pockels effect), which presently have been realized with poled polymer-liquid crystal guest-host-systems (cyanobiphenyl chromophores in PMMA)[2]. Poling of these polymers requires, however, high voltages (typically 100 V/cm), resulting in relatively weak nonlinearities, which are not very stable due to relaxation of the chromophore alignment. These problems could be overcome, in principle, with spontaneously SH-active or (anti-)ferroelectric liquid crystals like the here investigated B7 or B2 mesophases.
[1] R. Macdonald, F. Kentischer, P. Warnick and G. Heppke; Phys. Rev. Lett. 81: 4408 - 4411,1998.
[2] G. Priebe, K. Kunze, F. Kentischer, R. Schulz, O. Morales, R. Macdonald and H. J. Eichler; Proceedings of SPIE’s 45th Annual Meeting, San Diego, 2000. 4107: 9 - 18, 2000.