The laser systems currently used in ophthalmology either have some pulse length dependent side effects or are very expensive due to their complexity. Therefore, a newly developed approach using picosecond laser sources is investigated. These lasers combine the advantages of the low price of currently used short-pulse laser sources with the cold material ablation possibilities of high-end femtosecond sources. The surgeries intended are laser iridotomy, capsulotomy/post-cataract treatment and selective laser-trabeculoplasty (SLT). They are demonstrated on post mortem porcine eyes. The result is a more precise, less frayed tissue ablation with picosecond pulses in comparison to nanosecond pulses. The pulse energy could be reduced to (50 20) µJ per pulse instead of 1mJ to 10mJ per pulse, which is currently applied. The study of shock waves and cavitation bubbles revealed a huge difference in pressure between picosecond pulses (0:25MPa at 50 µJ) and nanosecond pulses (37MPa at 5 mJ). Therefore, the risk of collateral damage leading to potential additional clinical patterns and adverse effects could be significantly reduced.
We demonstrate sub-100 ps pulses with a Yb3+:YAG microchip laser passively Q-switched by a Cr4+:YAG saturable absorber. By introducing a subcavity, the laser threshold and the saturation energy are decreased which helps to prevent damage and to vary the effective emission and absorption cross sections. Pulse widths of 84 ps, repetition rates of 3.3 kHz and pulse energies of 32 μJ are achieved. This allows direct micromaterial processing e.g. for ophthalmic surgeries. To the best of our knowledge, this is the first sub-100 ps Yb3+:YAG/Cr4+:YAG microchip laser. A new approximation is used to calculate the rate equations for multiple longitudinal modes and to determine the threshold for single-longitudinal-mode operation.
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