Photorefractive keratectomy (PRK) is a laser-based surgical procedure that corrects near- and farsightedness by re- moving part of the lens of the eye to change its curvature and hence focal length. This procedure can remove layers 0.25 mm thick using pulses lasting 12.0 ns from a laser beam of wavelength 193 nm. Low-intensity beams can be used because each individual photon has enough energy to break the covalent bonds of the tissue. (a) In what part of the electromag- netic spectrum does this light lie? (b) What is the energy of a single pho- ton? (c) If a 1.50 mW beam is used, how many photons are delivered to the lens in each pulse?

Photorefractive keratectomy (PRK) is a laser-based surgical procedure that corrects near- and farsightedness by re- moving part of the lens of the eye to change its curvature and hence focal length. This procedure can remove layers 0.25 mm thick using pulses lasting 12.0 ns from a laser beam of wavelength 193 nm. Low-intensity beams can be used because each individual photon has enough energy to break the covalent bonds of the tissue. (a) In what part of the electromag- netic spectrum does this light lie? (b) What is the energy of a single pho- ton? (c) If a 1.50 mW beam is used, how many photons are delivered to the lens in each pulse?

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