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# hw5 - ECE 414 Spring 2011 Homework#5 Out Due(1 In the...

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ECE 414, Spring 2011 Homework #5 Out: 03/10/2011 Due: 03/22/2011 (1) In the diagram shown below, the pump P 2 (i.e., electrons, flash lamp, another laser, etc.) excites atoms from state 0 to state 2, nothing to state 1. To make the problem simple and tractable, assume state 0 is not depleted to any significant extent for any time (i.e., dN 0 /dt=0); use the simple decay route indicated; neglect stimulated emission; assume 1 = 2 μs and 2 = 1 μs; and let P 2 =10 20 cm -3 s -1 . Use symbols for (a) and (b) and find numerical values for (c) and (d). (a) What are the rate equations for states 2 and 1? (b) Give an expression for the densities N 2,1 as a function of time. (c) Over what time interval t is the population difference N 2 -N 1 > 0? (d) What are the steady-state populations in 2 and 1? (2) Consider the atomic system shown below being irradiated by an external wave tuned to the center of the 2 1 transition with 1 being the ground state. The wave pumps the atoms from 1 to 2 and also stimulates the atoms back to 1 from 2. In addition, the atoms in state 2 decay back to 1

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