Frequency doubling xerogels with ferroelectric particles

Abstract

Nonlinear optical single crystals are exploited for electro-optic, piezoelectric and pyroelectric devices [1]. The most commonly used nonlinear optical effects are second order: frequency doubling (second harmonic generation, SHG). LiNbO3 and KNbO3 single crystals are suitable frequency doublers under phase-matching conditions. Because of the time-consuming growth and the complex phase-matching of single crystals a new field of research has been established in the last decade: the new focus is on random materials, which are useful for optical applications [2,3]. We synthesized new functional SiO2 and TiO2 xerogels with nonlinear optical properties by incorporation of nano to micron sized particles of ferroelectric character. The silica and titiania wet gels are prepared by a sol-gel technique with TEOS (tetra-ethylorthosilicate) and TBOT (tetra-butylorthotitanate) as precursors [4,5]. A special ambient drying method was developed to produce crack-free highly transparent xerogels. Ferroelectric particles, such as BaTiO3, KNbO3, LiNbO3, LiTaO3, having sizes of around 100 nm up to 1 µm are embedded into the transparent matrix before the colloidal formation and gelation starts [6]. We observed frequency doubling at an incident wavelength of 1064nm and the possibility to continuously modify the refractive index of the xerogels over a wide range from 1.2 to 2.1. The refractive index matching is important to avoid light scattering and reduce the turbidity of the compound xerogels. [1] Günter, P.: Nonlinear Optical Effects and Materials. Springer, Berlin (1999) [2] Skipetrov, S. E.: Disorder is the new order. Nature vol. 432, p. 285 (2004) [3] Wiersma, D. S., Cavalieri, S.: A temperature-tunable random laser. Nature vol. 414, p. 708 (2001) [4] Hüsing, N., Schubert, U.:Aerogele - luftige Materialien: Chemie, Struktur und Eigenschaften. Angewandte Chemie Int. Ed. vol. 37, p. 23 (1998) [5] Pierre, A.C., Pajonk, G.M.: Chemistry of Aerogels and Their Applications. Chem. Rev. vol. 102, p. 4243 (2002) [6] Lisinski, S., Schaniel, D., Ratke, L., Woike, Th.: Second-Harmonic Generation by Ferroelectric Microparticles in Aerogels. Chemistry of Materials vol. 18, p. 1534 (2006)