Fundamental limits on third-order molecular susceptibilities

By the use of sum rules, the largest third-order molecular nonlinear-optical susceptibilities allowed by quantum mechanics are determined. The theoretical upper limit is found to depend only on the first excited-state transition energy and on the number of electrons, in agreement with experimental data. (C) 2000 Optical Society of America. OCIS codes: 190.0190, 160.0160, 160.4330.