Acoustic focusing associated with excimer laser ablation of the cornea

Focusing, as well as diffraction effects experienced by the stress wave produced by the argon-fluoride excimer laser ablation of corneal tissue have been studied in artificial and real eye samples; The evolution of the laser-induced acoustic front was imaged by means of fast shadowgraphy in an artificial eye model, while the absolute temporal profile of the pressure transient along the optical axis was directly measured in enucleated porcine eyes by a needle hydrophone inserted into the eyeball. Observations pointed out that the finite size of the acoustic source gave rise to diffraction effects during propagation, as the development of a negative tensile phase in the pulse shape, while the spherical shape of the acoustic source produced focusing of the wave front, causing pressure enhancements up to a factor of 3 in real eyes. The implications to surgical laser procedures as photorefractive keratectomy are discussed. (C) 1998 American Institute of Physics