Equations · equation
Einstein A and B Coefficients
Photonics · 1917
- Equation
- A₂₁/B₂₁ = 8πhν³/c³
- Field
- Photonics
- Named After
- Albert Einstein
- Year
- 1917
Symbols
A₂₁ rate of spontaneous emission · B₂₁ rate of stimulated emission per unit radiation density · ν frequency of the transition · h Planck constant · c speed of light
Significance
Einstein's thermodynamic bookkeeping of light and atoms demanded a third process nobody had seen: an incoming photon can tickle an excited atom into emitting an identical twin — same direction, same phase. Stimulated emission sat as a curiosity for four decades, then became the L, A, S, E and R of 'laser'.
Referenced by
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event
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