Single Crystal Films and Waveguides of Organic Materials: Preparation and Nonlinear Optical Properties

The objective of this program is to establish a generic method for the growth of thin single crystal films of important organic nonlinear optical materials and measurement of their nonlinear optical properties. Through the last years effort we have successfully prepared single crystal films of three organic materials which are i N-4-Nitrophenyl-L-prolinol abbreviated as NPP, ii 2-cyclooctylamino-5-nitropyridine, abbreviated as COANP, iii 4-N, N- dimethylamino-4-N-methylstilbazolium toluene-p-sulfonate, abbreviated as DAST. These materials have very large second order susceptibilities. Both NPP and COANP have an amphiphillic molecular structure, while DAST is an organic molecular salt. The single crystal films were prepared by a method called the shear method , with appropriate choice of the growth conditions. The shear method involves crystal growth at an interface and was originally applied to the growth of polydiacetylene films. Our results show that using the principles involved in the shear method, if the growth conditions are properly optimized for each compound, then molecules other than diacetylene are possible to organize as single crystal films. The only major condition that needs to be satisfied for this method to be applicable is that the molecule must be of an elongated shape with polar chemical groups at one or both ends.