Experiments on ocular tissue ablation at 5.3 and 6.0 μm with the Los Alamos advanced FEL

We investigated the ablation characteristics of a picosecond free-electron laser and compared its ablation effects on ocular tissues at 5.3 μm and 6.0 μm. The Advanced FEL at Los Alamos, operating in the wavelength range 4-6 μm, was used for this study. The 10-μs macropulse consisted of ∼1000 micropulses, each approximately 15 ps in length and separated from one another by 9.2 ns. The FEL beam was passed through a series of attenuator and focused to a 200-μm spot in the sample with a 150-mm f.l. CaF2 lens. The energy in each macropulse ranged from 5 to 120 mJ. Five transplantable corneal-scleral buttons preserved in corneal storage media were used for this study. The tissue sample was positioned at the focused FEL beam for the ablation, and then fixed for histologic study. Corneal cuts made at 6.0 μm revealed a well-defined ablation boundary. The measured lateral zone of the tissue damage was 11 ± 2 μm. The integrity of the adjacent tissue was well maintained. By contrast, the ablation boundary of the corneal cuts made at 5.3 μm appeared to be very disruptive. The collagen fiber near the ablation was thermally denatured and lost its organized structure. The lateral dimension of such effect extended out to 220 μm beyond the intended cut into the surrounding tissues. We concluded that a short-pulsed laser operating at 6 μm may be a potentially effective tool for cutting ocular tissues