Lecture 8: Laser amplifiers

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Amplified spontaneous emission Spontaneous photon flux Filter and polarizer Input photon flux Spontaneous emission is a source of amplifier noise. It is relatively broadband, radiated in all directions, and unpolarized. Optics can be used at the output of the amplifier to limit the spontaneous emission noise to a narrow optical band, solid angle d and a single polarization. 108
Amplifier noise The ASE of a laser amplifier is directly proportional to the optical bandwidth of the amplifier. To increase the signal-to-noise ratio (SNR) at the amplifier output, the total noise power can be reduced to a minimum by placing at the output end of an amplifier an optical filter that has a narrow bandwidth matching the bandwidth of the optical signal. Because of the spontaneous emission noise, the SNR of an optical signal always degrades after the optical signal passes through an amplifier. The degradation of the SNR of the optical signal passing through an amplifier is measured by the optical noise figure of the amplifier defined as F o SNR in SNR out where SNRin and SNRout represent the values of the optical SNR at the input and output ends of the amplifier. 109
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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
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Two-level systems No matter how a
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Two-level systems Take the upward
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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 and 102: Three-level pumping The dependence
Page 103 and 104: Saturated gain in homogeneously bro
Page 105 and 106: Gain coefficients This represents t
Page 107: Amplified spontaneous emission T
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Lecture 8: Laser amplifiers

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