Theoretical Studies of the Nonlinear Optical Properties of L-Arginine Phosphate
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THEORETICAL STUDIES of the NONLINEAR OPTICAL PROPERITES of L-ARGININE PHOSPHATE C. A. Langhoff, Dow Chemical,
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This paper will present quantum calculations on the L-arginine part of the nonlinear crystal L-arginine The emphasis here will' be on understanding phosphate. the NLO properties in terms of the excited states of the system and accompanying charge movements in these Both the carboxylate and the guanidyl excited states. ends of the molecule contribute to the values of 0. The guanidyl seems to be the bigger contributor, but the contribution varies with the particular tensor The properties of the crystal will not be component. discussed here.
Introduction The number of nonlinear optical crystals has been growing in recent years. Several organic crystals have appeared and have generated The Nonlinear Optical Materials group considerable interest and promise. at Livermore Labs has shown that the deuterated version of L-arginine phosphate is a good candidate for use in doubling and mixing Nd laser harmonics[l-2]. Japanese workers have also studied the growth and optical This organic material can be grown in large properties of the crystal[3]. has many acceptable properties with regard to nonlinearity, crystals and absorption, and damage threshold. The group at Livermore [1-2] has shown that the bulk of the nonlinear susceptibility of these crystals is due to the L-arginine part of the This is evidenced by the fact that crystal and not the phosphate ion. several other crystals involving L-arginine without any phosphate show For the purposes of this study, we will significant NLO activity. The system will be treated concentrate solely on the L-arginine molecule. as an oriented gas as no consideration is taken of the local field factors. This paper specifically will deal with a theoretical study of the The intent is to excited state electronic properties of L-arginine. understand the origins of the nonlinearity in terms of excited state structure and charge transfer effects. The contribution of intramolecular charge transfer transitions is the accepted model of the origin of the Since L-arginine second order nonlinearity in organic molecules. chemically can be understood as having two possible contributing groups, the amino-carboxylate end and the guanidyl end, we have done calculations on two molecular pieces which mimic both ends of the arginine molecule. It is the intent of this paper to show how these molecular "pieces" contribute Do they contribute to the NLO properties of the entire molecule. independently or cooperatively? No attempt will be made here to calculate Mat. Res. Soc. Symp. Proc. Vol. 173. c1990 Materials Research Society
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and compare these theoretical properties to those measured in This will be the subject of a future paper.
the crystal.
Calculational Details The basic program was The calculations were done at the CNDO/S level. a modified version of one available from the Quantum Chemical Program Exchange(No. 333). Modifications were necessary to adjust
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