Lecture 16 - Lecture 16 Lecture 16 [reading assignment:...

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Lecture 16 1 © Jeffrey Bokor, 2000, all rights reserved Lecture 16 [reading assignment: Hecht, 13.1] L ight A mplification by S timulated E mission of R adiation Basic laser architecture: The key element in any laser is the gain medium (light amplification) The light intensity is increased as it passes through the gain medium. We can examine what happens in each of our 3 viewpoints of light: The next element is feedback by an “optical resonator” gain medium L I o I i I o e gL I i g : gain coefficient = – ray direction is preserved – photons are added with same , direction – wave is reinforced coherently input field output field L T 4-5% R 100% output output coupler RT HR R 95-96%
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Lecture 16 2 © Jeffrey Bokor, 2000, all rights reserved Light bounces back and forth between the mirrors. On each round trip , ~ 4-5% of circulating power leaks out. This is restored by the round trip gain . Laser Threshold Condition If the loss is, for example, 4%, and if , then the gain exceeds the loss, and the system oscillates. Power grows inside the resonator. Steady state? High power level saturates the gain. At a certain power level gain = loss.
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Lecture 16 - Lecture 16 Lecture 16 [reading assignment:...

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