stimulated emission

(noun)

The process by which an atomic electron (or an excited molecular state) interacting with an electromagnetic wave of a certain frequency may drop to a lower energy level, transferring its energy to that field.

Examples of stimulated emission in the following topics:

  • Lasers

    • A laser is a device that emits monochromatic light through a process of optical amplification based on the stimulated emission of photons.
    • It does so through a process of optical amplification based on the stimulated emission of photons.
    • This "induced" decay process is called stimulated emission.
    • In stimulated emission, the decaying atom produces an identical "copy" of the incoming photon.
    • In stimulated emission process, a photon (with a frequency equal to the atomic transition) encounters an excited atom, and a new photon identical to the incoming photon is produced.
  • Oscillator Strengths

    • In an earlier equation, the final term could be important if the $E_i-E_f \approx -\hbar \omega$ this corresponds to stimulated emission of radiation.
    • Except for the degeneracy factors for the two states, the Einstein coefficients will be the same, so we can define an oscillator strength for stimulated emission as well,
    • We can also separate the emission from absorption oscillator strengths
    • Because the second term is for stimulated emission.
  • Absorption

    • The positive contributions are true absorption and the negative ones correspond to stimulated emission.
  • Emission

    • Generally material has two routes for the emission of radiation: stimulated emission and spontaneous emission.
    • The spontaneous emission is independent of the radiation field.
    • Let's define the spontaneous emission coefficient, $j$.
    • Often the emission is isotropic and it is convenient to define the emissivity of the material per unit mass
  • Lasers

    • Having examined stimulated emission and optical amplification process in the "Lasers, Applications of Quantum Mechanics" section, this atom looks at how lasers are built.
  • Problems

    • You may neglect scattering and assume that the emission is in the Rayleigh-Jeans limit.
    • Show that if stimulated emission is neglected, leaving only two Einstein coefficients, an appropriate relation between the coefficients will be consistent with thermal equilibrium between an atom and a radiation field with a Wien spectrum, i.e.
    • Compare the power from the surface emission to the power lost as the neutron star spins down.
  • Einstein Coefficients

    • Kirchoff's law yields a relationship between the emission and absorption coefficients for a thermally emitting material, specifically $j_\nu = \alpha_\nu B_\nu$.
    • This relationship suggests some connection between emission and absorption at a microscopic level.
    • If we calculate the probability of absorption of a photon for example, we can use the Einstein relations to find the rate of stimulated and spontaneous emission.
    • Can you use the principle of detailed balance to say anything about the relationship between the stimulating and the stimulated photon?
  • Microwaves

    • A maser is a device similar to a laser, which amplifies light energy by stimulating photons.
    • The maser, rather than amplifying visible light energy, amplifies the lower-frequency, longer-wavelength microwaves and radio frequency emissions.
  • Calculating the Emission and Absorption Coefficients

    • We can write the emission and absorption coefficients in terms of the Einstein coefficients that we have just examined.
    • The emission coefficient $j_\nu$ has units of energy per unit time per unit volume per unit frequency per unit solid angle!
    • The Einstein coefficient $A_{21}$ gives spontaneous emission rate per atom, so dimensional analysis quickly gives
  • Problems

    • What is the synchrotron emission from a single electron passing through a magnetic field in terms of the energy density of the magnetic field and the Lorentz factor of the electron?
    • What is the inverse Compton emission from a single electron passing through a gas of photons field in terms of the energy density of the photons and the Lorentz factor of the electron?
    • What is the total inverse Compton emission from the region if you assume that the synchrotron emission provides the seed photons for the inverse Compton emission?
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