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 0.250?m thick in pulses lasting 12.0ns with a laser beam of wavelength 193nm . Low-intensity beams can be used because each individual photon has enough energy to break the covalent bonds of the tissue.
Part A What is the energy of a single photon? In eV
Part B If a 1.70mW beam is used, how many photons are delivered to the lens in each pulse?