Laser Physics Lecture -2

Definition of laser

  • A laser is a device that in the generates light by of a process called in the STIMULATED EMISSION.
  • in the acronym in the LASER stands for Light in the Amplification by in the Stimulated Emission of Radiation


  • in the Laser action is based on the amplification of a EM waves in the means of a forced r induced atoms or in the molecules  See by a diagram
  • in the laser radiation uses 3 fundamental in the phenomena when EM waves in the interact with the matter a namely.
  • See by diagram

Excited atoms emit photons spontaneously.
When an atom in the an excited in the state falls to a lower energy level, it emits a photon in the light.
in the Molecules a typically in the remain excited for no in the longer than a few in the nanoseconds. This is often also called in the fluorescence or, when it takes longer, in the phosphorescence.

Spontaneous absorption

  • Let us in the consider two in the energy level in the having energy in the E1 & E2 resp.
  • in the atom will remain in the ground state in the unless some in the external stimulant in the applied to it.
  • When an in the EM wave i.e photon of particular freq fall on it , there isin the  finite probability that in the atom will jump in the fin the in the form in the energy in the state E1 to E2.

Spontaneous emission

  •  in the  Consider an atom in the higher state (E2).
  • It can decay to lower energy in the level by an emitting in the photon.
  •  in the Emitted photon have in the energy hv=E2-E1.
  •  in the Life time of in the excited state is a 12-9sec.

Stimulated vs Spontaneous Emission
in the Stimulated in the  emission in the in therequires the presence of a photon.     An “incoming”in the photon stimulates a molecule in an excited in the state to in the decay to the ground state by in the emitting a photon.  in the stimulated photons in the travel in the samea the direction as in the incoming tg photon.
in the Spontaneous emission does not require  the presence of a photon.                                                                                  in the  Instead a molecule in the excited state in the  can relax to the ground in the  state by spontaneously in the  emitting a photon. in the  Spontaneously emitted in the  photons are emitted in all directions.

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