Mirrorless all-optical bistability in bacteriorhodopsin

We report direct observations of all-optical mirrorless bistability associated with saturable absorption in three kinds of bacteriorhodopsin (BR) samples: wild-type BR in water solution and dispersed in thin films of a polymer matrix as well as water solution of the genetically engineered mutant BRD96N. The experiments are carried out with picosecond pulses at 532 nm. The values measured for the saturation intensity are explained in terms of the relaxation of the excited M state population to the B state of the BR photocycle for the three kinds of samples studied.