Thin films, second-order nonlinear optics

Second-Order Nonlinear Optics in Chiral Thin Films... 

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

In this paper, an overview of the origin of second-order nonlinear optical processes in molecular and thin film materials is presented. The tutorial begins with a discussion of the basic physical description of second-order nonlinear optical processes. Simple models are used to describe molecular responses and propagation characteristics of polarization and field components. A brief discussion of quantum mechanical approaches is followed by a discussion of the 2-level model and some structure property relationships are illustrated. The relationships between microscopic and macroscopic nonlinearities in crystals, polymers, and molecular assemblies are discussed. Finally, several of the more common experimental methods for determining nonlinear optical coefficients are reviewed. 

Verbiest, T., Kauranen, M., Persoons, A.J. Second-order nonlinear optical properties of chiral thin films, Mater. Chem. 9, 2005-2012 (1999)... 

In last years one observes a fast progress in synthesis and elaboration of non-centrosymmetric functionalized polymers for applications primarily in electrooptic modulation and frequency conversion. These materials possess large second order nonlinear optical susceptibility x and can be easily processed into good optical quality thin films for travelling wave applications. Essentially four types of polymeric structures have been developed, as shown in Fig. 1 ... 

For the functionalized polymer DRGPMMA thin film we have studied with 0.7 pm thickness and the value of second order nonlinear optical susceptibility X -2(0 (o,(o) =120 pm/V as determined by second harmonic generation at 1.32 pm... 

Electrostatic layer-by-layer (LBL) self-assembly techniques based on oppositely charged poipelectrolytes can be useful to create stable noncentrosymmetric order in thin films. Using this interesting technique, thermodynamically stable noncentrosymmetric multilayer films can be prepared without any need for poling. Tripathy et al. reported the fabrication stable multilayer films of epoxy-based side chain azo polymers for second-order nonlinear optics.The second-order NLO coefficients of the five-bilayer LBL films of these polymers were found to be comparable to those of spin-coated poled films. A schematic view of the procedure to fabricate polyelectrolyte-based LBL films is shown in Fig. 7. 

Two complementary amphiphilic polymers woe alternatively deposited by Y-type deposition. In Polymer A, the chromophore s electron accepting end is connected to a hydrophobic bridging unit, and its electron donating end is connected to a hydrophilic bridging unit The converse is true for Polymer B. These multilayer thin films have second order nonlinear optical properties which are stable at ambient temperature in the absence of oxygen. Microstructural information on a 92-bilayer polymer film was obtained fix)m polarized optical measurements. 

Cui, Y., Qian, G., Chen, L., Wang, Z., and Wang, M. 2008. Second-order nonlinear optical properties of cross-linked silica films prepared through sol-gel process. Thin Solid Films 516 5483-5487. 

Table 3.13 A collection of reported second-order nonlinear optical susceptibilities (d coefficients) for bulk and thin-film ZnO.

Churikov, V. M., Hung, M. F., Hsu, C. C., Shiau, C. W, and Luh, T. Y. (2000). Encoding of macroscopic second order nonlinearity via all-optical polar alignment in substituted nor-bornene polymer thin films. Chem. Phys. Lett. 3 2, 19-25. 

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