ECE 4751 Old Final Exam Solutions

# ECE 4751 Old Final Exam Solutions - ECE 4751 Laser Theory...

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ECE 4751 Laser Theory and Applications Fall 2007 Dr. Klein Final Exam Instructions: (1) Closed book, closed notes. You are only permitted a calculator and a writing instrument. (2) Show all work to receive full credit. Proctor will provide additional paper on request. (3) Each problem is worth the number of points indicated (100 points total). (4) Circle, box, or otherwise indicate your final answer. (5) Answers must be legible. (6) Calculate numerical values where possible. (7) Read the problems carefully! They may be similar to problems you’ve seen before, but something has been changed. Useful constants: ε 0 = 8.854e-12 F/m μ 0 = 4 π x 1e-7 H/m η 0 = 377

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1. (15 points) Short answer. (a) In a Q-switched laser, the Q factor of a laser cavity is reduced and the active region of the laser is strongly pumped to achieve large optical gain. After this, the cavity Q is abruptly increased. Briefly sketch or describe the time evolution of the gain and the photon number after the Q is increased. (b) Find the approximate bandgap energy (in eV) of a semiconductor that emits green light. The wavelength is 510 nm.
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