Analysis of nonlinear absorption changes in reaction centers of photosynthetic bacteria as a result of selective excitation with high-power laser pulses

A theoretical analysis is made of nonlinear changes in the optical density of reaction centers of photosynthetic bacteria after excitation with high-power picosecond laser pulses. A simplified four-level model is used to show that changes in the optical density of such a system are independent of the phase memory parameter at very high excitation intensities. The results of numerical calculations of nonlinear changes in the optical density of reaction centers are in qualitative agreement with the experimental data. These results are sensitive to variation of both the phase relaxation time and of the dipole moments of optical transitions in the molecules which absorb the exciting radiation. The feasibility of determination of these parameters is demonstrated.