Advanced model for a 4-keto Bacteriorhodopsin photocycle based on phase grating recording analysis

Peculiarities of the phase grating recording in polymer films containing 4- keto Bacteriorhodopsin are investigated under absorption saturation. The ph ase-modulated beams technique is used to measure photoresponse from the fil ms in real time. Three maxima of the photoresponse are detected. The first two (at similar to 1 and similar to 10 s) correspond to the positive amplit ude of the phase grating, whereas the third maximum corresponds to the nega tive one (at similar to 1 min). This phenomenon is explained, as theoretica l analysis shows, by the spatial distortions of the grating, resulting in t he fundamental spatial harmonic sign exchange. These maxima, we believe, co rrespond to three photocycles in the 4-keto Bacteriorhodopsin molecule, for which a novel scheme is suggested. The results of theoretical simulations are shown to be in good agreement with the experiment.