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.
- 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.
- 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.