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Dynamic hologram recording and relaxation in C60 solutions

We performed numerical experiments on dynamic hologram (grating) recording and relaxation in fullerene C60 solutions and carried out the comparison with experiment on self-diffraction (intensity up to 50 MW/cm2, pulse duration 10nm, wavelength 532 nm, angle between pump beams 0.16 rad). The grating recording was numerically simulated by the differential equations: (1) balanced equations system describing population in six-level system, (2) time-space equation for absorption from different levels, (3) equation for the hologram thermal relaxation. Using this method the time-space dependence of medium refraction index due to thermal absorption was determined. Based on phase grating recording the estimation of diffraction efficiency in different diffraction orders was determined. It was shown that during the recording the shape of phase thermal grating becomes nearly rectangular due to absorption on exited singlet and triplet sublevels. The long time of life of triplet sublevels of C60 influences phase grating relaxation. The calculated values of diffraction efficiency in 1-5 levels are almost equal to the values form the experiment. According to our results of numerical analysis we can make a conclusion that the model successfully describes recording and relaxation of thermal phase hologram in fullerene solution. Results of phase grating relaxation can be used for investigation of fullerene properties and life-times of triplet sublevels. Our model can be used for numerical simulation of phase and amplitude grating recording and relaxation in fullerene solution and fullerite with pumping by nano-pico and femtosecond pulses and CW radiation.