In this paper

we first presented the third-order optical nonlinearity and excited state relaxation process of phycocyanin using degenerated four-wave mixing(DFWM)and time-resolved degenerated four-wave mixing. The χ

(3)

value of phycocyanin is 1.2×10

-11

esu. By fitting its response curve of time-resolved DFWM

we obtained its relaxation lifetime is 308 ps. The third-order optical nonlinearity and excited state relaxation of phycocyanin come from the reaction among its submolecules or pyrrole molecules.