lemental analyses of selected stilbazolium compounds reported in Table 1 of the paper. The cation is identified the number of the aldehyde precursor in Fig. 2. of the paper, followed by the counterion of interest and then molecular formula is given. At the right the percentages for carbon, hydrogen and nitrogen is given; for each salt, the upper value (to the right of the molecular formula) is the expected value and immediately below that is the experimentally determined value. Elemental analyses were performed by the California Institute of Technology Analytical Facility.

We report optical rectification and subsequent generation of subpicosecond submillimeter-wave radiation from a nonlinear organic crystalline salt. With optical excitation at a wavelength of 820 nm and a 150 fs pulse duration, the magnitude of the rectified field from the organic salt dimethyl amino 4-N-methylstilbazolium tosylate is one and two orders of magnitude larger than that from GaAs and LiTaO3 crystals, respectively. This organic crystal presently provides the most intense terahertz radiated field among all of the natural nonexternally biased materials we know.

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ABSTRACFSingle crystals of the organic salt 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) are shown to exhibit large second harmonic generation and electro-optic coefficients. Maker fringe second harmonic generation measurements at 1907 nm give di 1 = 600 200 pm/V and electro-optic modulation measurements at 820 nm give ri 1 400 150 pm/V. These initial results as well as preliminary results on the refractive indices, dielectric constants, transparency, and thermal stability of DAST suggest that it and related organic salts are promising materials for electro-optic device applications. INTRODUCFIONThere is considerable interest in materials with large second order nonlinear optical susceptibilities, 1 Such materials can be useful for frequency conversion of lasers and electro-optic modulation of optical radiation, leading to possible applications in optical communication, optical image processing, and phased array control systems. Key issues in the development of organic materials with large (2) nonlinearity are molecular engineering of large hyperpolarizability,2 , and noncentrosymmetric assembly of high molecules at high number density into bulk structures.3 Crystalline materials have maximal packing densities but the crystalline packing of neutral dipolar molecules is usually centrosymmetric. Meredith4 and more recently Marder, et al. and Nakanishi, et al.1045 have demonstrated that highly nonlinear stilbazolium cations can be crystallized with various anions leading in many cases to salts with large macroscopic nonlinearity, as evidenced by powder SHG efficiencies. This "salt methodology" offers the routine generation of different packing arrangements of the same ionic nonlinear chromophore, facilitating the search for optimal packing. Additionally, the ionic chromophores are packed at high number density and salt crystals can be robust compared to crystals of neutral molecules.In order to determine whether the large powder SHG efficiencies exhibited by many stilbazolium salts will be manifested in practically useful nonlinearities, we have undertaken the growth of single crystals of promising salts and the characterization of their nonlinear optical coefficients. Of the various stilbazolium salts examined to date the tosylate salt of dimethylaminostilbazolium (DAST), whose molecular structure is shown below, exhibited the H3 j-N' ' -+ H3d -1N-CH -03S-O.-CH3 Figure 1. Structure of 4'-dimethylamino-N-methyl-4-stilbazolium tosylate. 302 / SPIE Vol. 1560 Nonlinear Optical Properties of Organic Materials lV(1 991) O-8194-0688-b/91/$4.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 07/12/2015 Terms of Use: http://spiedl.org/terms