Question

A laser can be made by placing a light source in an optical resonant cavity which has two highly reflective flat mirrors at its ends. Light produced by the source will reflect back and forth from the end mirrors and so produce standing waves. Assume that the mirrors at the ends of the cavity are nodes of the standing wave pattern. (a) What are the frequencies of the normal modes of the cavity in terms of the distance L between the mirrors and the speed of light c? (b) Suppose that the light source emits light with frequencies in the range ν0 ± δν, where ν0 = 5 × 1014 Hz and δν = 1 × 109 Hz. How many normal modes are in this frequency range if the length of the cavity is 1.5 m? (c) What is the maximum cavity length for which only one mode will be excited (i.e., so that the laser will emit light of only one frequency)?

Answer 1

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