Strong self-defocusing effect and four-wave mixing in bacteriorhodopsin films

Abstract

We find strong self-defocusing in bacteriorhodopsin films in the near IR with powers in the tens of milliwatts. The defocused beam acquires a ring pattern because of spatial self-phase modulation. We also demonstrate efficient four-wave mixing with phase-conjugate reflectivities of 26%. We discuss the origin of this high nonlinearity.