Questions for Week Four—Lasers
Write well-reasoned verbal answers
to these questions. You should be able to find the base for your answer in the
week’s readings, but the questions are not directly answered there. You have to
think them out, using the facts and concepts from the reading. Calculations are
not necessary, though if you find it useful, include them by all means. Make
sure your prose is clear and complete. One or two paragraphs should be enough
for each question.
(1) In figure 9-36, why does the laser beam exit the concave mirror as a parallel beam? (Drawing a figure might help)
(2) Explain how decreasing the probability of collision with the cavity wall might reduce the population inversion and decrease laser gain.
(3) What is the function of helium in a helium-neon laser? Why not just use neon?
(4) One of the reasons lasers are popular in science fiction and the like is their ability to ‘melt through steel’, yet the caption for the picture on page 430 states that laser light ‘cools the atoms’. Can both these phenomena be true? If so, how?
(5) Using what you know about lasers, explain how a maser works. Why do you think the implementation of masers came about before optical lasers? (A few hints to get you started: Microwave radiation, with wavelength on the order of 1 cm, is emitted by a maser. Think of what kind of transitions are involved when a photon of this wavelength is absorbed/emitted versus the type of transition involved in laser action, in which light of visible wavelength is typically emitted. Also, consider the requirements to construct a cavity of the appropriate length in each case.)