Organic materials are expected to have relatively strong nonlinear optical properties due to delocalized electrons at
\pi-\pi
L-arginine is one of the essential amino acids widely distributed in biological substances. It forms a number of salts with organic and inorganic acids showing non-linear optical properties. L-Arginine maleate dihydrate (C6H14N4O2,C4H4O4,2H2O) is one of these L-arginine salts which is a complex of strongly basic amino acid, carboxylic acid and provides useful information in relation to molecular interaction in present-day biological systems and to prebiotic self-organisms.[1] It is also a nonlinear optical material with second harmonic generation efficiency 1.68 times that of KDP.[2] L-arginine maleate dihydrate crystals are grown from solution by solvent evaporation; they belong to the triclinic space group P1.
L-methionine L-methioninium hydrogen maleate also belongs to the amino acid family. Crystals are grown by slow evaporation of an aqueous solution containing L-methionine and maleic acid, resulting in centimeter-large crystals of a non-centrosymmetric space group.[3] They were applied for second-harmonic generation of an (wavelength 1064 nm), and SHG efficiency equal to that of KDP has been obtained.