Abstract

Third-order nonlinear optical susceptibilities χ⁽³⁾ were measured for the photodynamic protein complexes bacteriorhodopsin (BR), phycocyanin (PC), and B-phycoerythrin (PE) in water and deuterium oxide by using the technique of degenerate four wave mixing with picosecond pulses at 532 nm. From the measured values of χ⁽³⁾ we obtained the second hyperpolarizability <γ>. These values are for <γ> (BR) = 6.7 × 10⁻³⁰, <γ> (PC) = 9.8 × 10⁻³⁰, and <γ> (PE) = 7.0 × 10⁻²⁹ esu, and the corresponding χ⁽³⁾ values calculated for pure samples are 6.5 × 10⁻¹⁰, 1.2 × 10⁻⁹, and 9.0 × 10⁻⁹ esu. Thin film measurements for BR in polyvinyl alcohol matrix also yielded about the same values. After exposure to the green laser light for 1-2 min, the samples of phycocyanin and B-phycoerythrin are bleached and the phase conjugate signal disappears; the signal returns to the original state after 24 h. In the case of bacteriorhodopsin the response is too fast to be observed with our system.

© 1992 Optical Society of America