Photoinduced nonlinear refraction in a polymeric film encapsulating a bacteriorhodopsin mutant

The absorption change versus time after switching off the illumination on a polymeric film that contained a bacteriorhodopsin (BR) mutant has been measured. The M-lifetime of this BR mutant is $∼320s$⁠. A pertinent Z-scan was performed to study the BR optical nonlinearity. A physical model with multi-level transitions in the Z-scan was suggested. The minimum saturated light intensity measured at 633 nm is $∼0.9mW/cm2$⁠. A low intensity of $70μW/cm2$ has been used for recording in this film. The change in refraction index $Δn633$ is $−3.0×10−3$ and $Δn476$ is $8.5×10−3$ with the intensity all at $∼100mW/cm2$⁠.