Nonlinear optical characterization of retinal molecules

The measurements on the nonlinear absorption coefficient for the whole retina and separated molecular components have been determined using open-aperture z-scan. Our recent retinal damage studies have shown that the threshold for retinal damage decreases below one nanosecond. Laser-induced breakdown has been implicated in the threshold-level mechanism for damage. The threshold is reduced below 100 fs, where LIB is the damage mechanism. Our hypothesis for this experiment is that non-linear optical properties of the constituents of the retina will affect the absorption coefficient of the retina for ultrashort pulse laser exposure and lower the retinal damage threshold for these exposures by lowering the laser-induced breakdown threshold in the tissues. This suggests that nonlinear absorption effects should be considered in the analysis of any data that relate energy deposition rates from laser exposures in tissue to thermal or photomechanical damage mechanisms for cell death. We describe the impact of these measurements on retinal damage thresholds and damage mechanisms for various pulse regimes.