prelim2

# prelim2 - population difference between level I and level...

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1. The laser below has an output intensity of 1000 Wcm2. n flr=10% llE'' u !-'-''[ ll -->ro"=1ooov/ lffil ECE 4300 Preliminary Exam 2b November 19, 2008 Instructions: You have 50 minutes to complete this exam. You may use notes, a calculator, and your textbook, should you feel the urge. Attempt all problems. a. If the cavitybeamwaist is in the gain medium, and the actual laser output power is 10 W, what is the beamwaist, roo? b. What is the total intensitv of the laser mode inside the laser cavity? c. Estimate the threshold gain for this laser, y*. 2. A two-level system is used as a saturable absorber to Q-switch a laser. The upper level has only radiative relaxation process, with Ar,:107 sec-l. Assume at t:0 all the population resides in level 1, with value [N]. E2 "aor', I -El A beam of light is suddenly incident on the saturable absorber, and the photon energy is equal to Er-E,. Assume the pulse

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Unformatted text preview: population difference between level I and level 2long after the beam has started (t )) rupp.,.t t ) b. The instantaneous population of Nr(t) as a function of time. a J. The laser cavity shown below has a 4level gain medium, with the energy level configuration as shown. When the laser is pumped hard enough to generate 10 w of output power, as shown, the laser gain medium generates 100W of heat, which has to be removed by a heat sink. The upper laser level (2.5 eV) is the source of a lot of spontaneous emission, which escapes from the gain medium, as well as stimulated emission that contributes to the output beam. You may assume that all transitions from the 2.5 eY state to 0.5 eV state are radiative - there is no non-radiative decay from the 2.5 eY level. {-I I .t, V-tEr l*0.'-l I I 0eV How much energy is supplied by the pump to this system? What is the unsaturated gain of the medium, yo? T=10o/o 3 eV->Pou,=10W Pump 2.5 eV 0.5 eV ffi a. b....
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## This note was uploaded on 07/09/2009 for the course M&AE 326 taught by Professor Psiaki during the Spring '08 term at Cornell.

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prelim2 - population difference between level I and level...

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