Teaching Physics with the Physics Suite

Edward F. Redish

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Laser eye surgery

Laser eye surgery is carried out by delivering highly intense bursts of energy using electromagnetic waves. A typical laser used in such surgery has a wavelength of 190 nm (ultraviolet light) and produces bursts of light that last for 1 ms. It delivers an energy of 0.5 mJ to a circular spot on the cornea with a diameter of 1 mm. (The light is well approximated by a plane wave for the short distance between the laser and the cornea.)

  1. Assuming the energy of a single pulse is delivered to a volume of the cornea about 1 mm3, and assuming the pulses are delivered so quickly that the energy deposited has no time to flow out of that volume, how many pulses are required to raise the temperature of that volume from 20 C to 100 C? (Assume that the cornea has a heat capacity similar to that of water.)

  2. Estimate the maximum strength of the electric field in one of these pulses.

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Page last modified October 23, 2002: OP06