Lecture 8: Laser amplifiers

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Three-level pumping We can write the population difference in the usual form N N 0 1 s W i N 0 N a ( sp W 1) 1 sp W s 2 sp 1 sp W As in the four-level scheme, N 0 and s saturates as the pumping transition probability W increases. 102 102
Saturated gain in homogeneously broadened media The gain coefficient () of a laser medium depends on the population difference N. N is governed by the pumping level. N depends on the transition rate W i . W i depends on the photon-flux density . => the gain coefficient () of a laser medium is dependent on the photon-flux density that is to be amplified. This is the origin of gain saturation and laser amplifier nonlinearity. 103
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Lecture 8: Laser amplifiers Opt
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Optical transitions 3
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Photon-matter interaction processes
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Three basic photon-matter interacti
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Probability per second of a spontan
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Spectral lineshape The spectra
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Homogeneous broadening If all o
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Inhomogeneous broadening Howeve
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Transition rates The transiti
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Transition rates For the upward tr
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Transition rates The total induce
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Blackbody radiation A system und
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Planck’s law of blackbody radiati
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Transition rates In thermal equili
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Boltzmann distribution Energy E E 2
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Transition rates Therefore, the s
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Transition cross section For the
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Optical absorption and amplificatio
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Optical absorption and amplificatio
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Resonant optical susceptibility Fo
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Resonant optical susceptibility Th
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Population inversion 43
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Population inversion A nonequilibr
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Rate equations The net rate of chan
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Population inversion Population in
Page 51 and 52: Two-level systems No matter how a
Page 53 and 54: Two-level systems Take the upward
Page 55 and 56: Two-level systems Intuitively, th
Page 57 and 58: Quasi-two-level systems By pumpi
Page 59 and 60: Population inversion in three-level
Page 61 and 62: Three-level systems The parameter
Page 63 and 64: Four-level systems pump h p Nonradi
Page 65 and 66: Neodymium-doped glass Nd 3+ :glass
Page 67 and 68: Coherent optical amplifiers Gain, n
Page 69 and 70: Coherent light amplification As
Page 71 and 72: Population inversion Light tran
Page 73 and 74: Real coherent amplifiers Real
Page 75 and 76: Gain and bandwidth The wave is am
Page 77 and 78: Gain coefficient As the incident
Page 79 and 80: Gain coefficient The coefficient
Page 81 and 82: Gain bandwidth The dependence
Page 83 and 84: Phase‐shift coefficient The las
Page 85 and 86: Rate equations 2 R 2 1/ 21 = 1/ sp
Page 87 and 88: Rate equations in the absence of am
Page 89 and 90: Rate equations in the presence of a
Page 91 and 92: Four-level pumping Pump R Laser W i
Page 93 and 94: Four-level pumping In most four-le
Page 95 and 96: Four-level pumping Under these c
Page 97 and 98: Three-level pumping Rapid decay S
Page 99 and 100: Three-level pumping The population
Page 101: Three-level pumping The dependence
Page 105 and 106: Gain coefficients This represents t
Page 107 and 108: Amplified spontaneous emission T
Page 109: Amplifier noise The ASE of a la
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Lecture 8: Laser amplifiers

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