Photorefractive keratectomy (PRK) is a laser-based surgery process that corrects near- and farsightedness by removing part of the lens of the eye to change its curvature and hence focal length. This procedure can remove layers 0.025 micrometers (E-6) thick in pulses lasting 12ns with 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 electromagnetic spectrum does this light lie?

b) What is the energy of a single photon?

c) if a 1.35 mW beam is used, how many photons are delivered to the lens in each pulse?