Second and Third Order Nonlinear Optical Properties of Crystalline Inorganic / Organic Complexes
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SECOND AND THIRD ORDER NONLINEAR OPTICAL PROPERTIES OF CRYSTALLINE INORGANIC / ORGANIC COMPLEXES. HENRY 0. MARCY*, LESLIE. F. WARREN*, LAURA E. DAVIS**, MARK S. WEBB**, AND STEPHAN P. VELSKO** *Rockwell International Science Center, P.O. Box 1085, Thousand Oaks, CA 91358 **Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550
ABSTRACT The properties for members of a new class of nonlinear optical (NLO) materials which stoichiometrically incorporate organic and inorganic constituents into a single crystalline lattice are reported. Recent results for our synthetic, crystal growth, and optical studies suggest that a number of these relatively transparent "semiorganic" compounds have significant second and/or third order NLO responses and often display favorable crystal growth morphologies. The prototype material of this class, zinc tris(thiourea) sulfate, or ZTS, has a UV cutoff at about 325 nm, can be readily grown to cm 3 sizes, and has been shown to be a highly efficient Type 1Rfrequency doubler for 1064 nm Nd:YAG laser radiation. ZTS also possesses a moderate third order nonlinear optical response (ca. 0.1 x CS2) which occurs on at least a picosecond time scale as determined by degenerate four-wave mixing (DFWM) experiments at 532 nm. Refractive index, second harmonic generation, and DFWM data for a number of these new compounds are presented.
INTRODUCTION Organic materials have been the primary focus of new nonlinear optical (NLO) materials development efforts for the past decade as a result of their often large second and third order optical nonlinearities and inherent chemical design flexibility. 1-4 However, implementation of single crystal organic materials in practical device applications has been impeded by their often inadequate transparency, poor optical quality, lack of robustness, low laser damage threshold, and an inability to grow large-size crystals. The molecules in pure organic crystals are often coupled only by relatively weak van der Waals forces or hydrogen bonding, which results in rather poor mechanical properties. Even for very promising and well characterized organic second harmonic generation (SHG) materials, large scale growth is often difficult; quality can be compromised due to solvent impurity incorporation during crystallization, and absolute purification of the growth solution can be difficult. Ideally, the large nonlinearities of pi-conjugated organics and the favorable crystal growth characteristics and mechanical properties of ionic inorganic salts would be married into a single NLO crystal. 5 "7 The extended pi-conjugation networks in the organic systems with the largest nonlinearities (e.g., powder-SHG intensities up to 1000 x urea 8 ) invariably have significant absorption in the visible portion of the spectrum. Consequently, for applications such as frequency conversion into the blue/near U.V. regions, more transparent and less extensively delocalized organics must be studied (e.g. urea), and alternative methods of enhancing the nonlinearities (e.g., optim
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