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Multibeam Technique Improves Eye Surgery, Machining

Photonics Spectra
May 1997
Kathleen G. Tatterson

WERMELSKIRCHEN, Germany -- Many excimer laser beams are better than just one, at least for laser eye surgery and for precise laser machining, according to the scientists who developed a new excimer laser technique.
Surgeons can correct many vision problems by using excimer laser beams to reshape the cornea, and industry uses excimer beams to precisely machine surfaces. Commercial excimer laser systems use lasers with typical pulse energies of 22 to 300 mJ, but homogeneity is difficult to maintain at high energy levels.
In surgery, the interaction between the beam and the corneal tissue can cause hydration-related effects that produce flaws. Higher repetition rates would improve some errors, but the lasers that can attain these rates are limited to microjoule energies.
To ablate material more smoothly, a team from Kera Technology Inc. of Fremont, Calif., and the Institute of Ophthalmology in Madrid, Spain, developed a multibeam, random-projection technique that ensures homogenous energy distribution.
The method splits a laser pulse to form an even number of small spots that are spatially out of phase and diametrically positioned. The system moves the beams randomly over an object until it has covered the entire surface.

Technology integrated
ATL Lasertechnik GmbH has integrated the technology into its air-pulsed ATLEX SP laser. The research team used the ATLEX SP at 193 nm with 4 mJ of power and a 200-Hz repetition rate. The beam passed through an attenuator, a 600-mm focal lens, a beamsplitter and two galvanometer pairs. A mirror directed the beam with a 1 3 0.8-mm spot onto polymer buttons and cadaver eyes. The laser ablated 0.15 µm of material per pulse.
The procedure produced refractive changes of up 20 diopters in astigmatic specimens, and corneal topography showed homogeneous ablation across the treated area.
The device will undergo medical approval processes this year.

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