Threshold energies in the artificial retina

Laser threshold energies for artificial retinal damage from ultrashort (i.e. less than or equal to 1 ns) laser pulses are investigated as a function of both pulse width and spot size. A piece of film acts as the absorbing layer and is positioned at the focus of the Cain artificial eye (17 mm in water). We performed experiments at the focal point, and at two and ten Rayleigh ranges in front of the focus with the damage endpoint being the presence of a bubble coming off the film. Thresholds were determined for wavelengths of 1064 nm, 580 nm, and 532 nm with pulse durations ranging from the nanosecond (ns) to the femtosecond (fs) regimes. For the at-focus data in the visible regime, the threshold dropped from 0.25 (mu) J for a 5 ns pulse at 532 nm to 0.11 (mu) J for a 100 fs, 580 nm pulse. Similarly, for the near infrared (NIR) the threshold changed from 5.5 (mu) J for a 5 ns pulse to 0.9 (mu) J for a 130 fs pulse. These results are discussed in the context of applicable nonlinear optical phenomena.