Lecture 8: Laser amplifiers

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Population inversion and optical gain Population inversion is the basic condition for the presence of an optical gain. In the normal state of any system in thermal equilibrium, a low-energy state is always more populated than a high-energy state – no population inversion Population inversion in a system can only be accomplished through a process called pumping – actively exciting the atoms in a low-energy state to a high-energy state. Population inversion is a nonequilibrium state that cannot be sustained without active pumping. To maintain a constant optical gain we need continuous pumping to keep the population inversion at a constant level. Many different pumping techniques depending on the gain media: optical excitation, current injection, electric discharge, chemical reaction, and excitation with ion beams 44
Population inversion A nonequilibrium distribution showing population inversion Energy E E 2 E 1 N 1 N 2 Population N 45
Page 1 and 2: Lecture 8: Laser amplifiers Opt
Page 3 and 4: Optical transitions 3
Page 5 and 6: Photon-matter interaction processes
Page 7 and 8: Three basic photon-matter interacti
Page 9 and 10: Probability per second of a spontan
Page 11 and 12: Spectral lineshape The spectra
Page 13 and 14: Homogeneous broadening If all o
Page 15 and 16: Inhomogeneous broadening Howeve
Page 17 and 18: Transition rates The transiti
Page 19 and 20: Transition rates For the upward tr
Page 21 and 22: Transition rates The total induce
Page 23 and 24: Blackbody radiation A system und
Page 25 and 26: Planck’s law of blackbody radiati
Page 27 and 28: Transition rates In thermal equili
Page 29 and 30: Boltzmann distribution Energy E E 2
Page 31 and 32: Transition rates Therefore, the s
Page 33 and 34: Transition cross section For the
Page 35 and 36: Optical absorption and amplificatio
Page 37 and 38: Optical absorption and amplificatio
Page 39 and 40: Resonant optical susceptibility Fo
Page 41 and 42: Resonant optical susceptibility Th
Page 43: Population inversion 43
Page 47 and 48: Rate equations The net rate of chan
Page 49 and 50: 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 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 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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