Some of the differences between spontaneous and stimulated emission of radiation are
given as follows:
1. In spontaneous emission, an atom in excited state falls to the ground state on its own without any incident photon while in stimulated emission transition takes place by stimulating photons or by an external agency.
2. In stimulated emission for each incident photon there are two outgoing photons in
the same direction while in spontaneous emission the emitted photons move
randomly in any direction.
3. The photons emitted in spontaneous emiss ion have a random phase and hence are
incoherent while in stimulated emission the emitted photons are in phase and
hence are coherent.
4. The rate of spontaneous emission is proportional to only the number of atoms in
the excited state while the rate of stimulated emission is proportional to the
number of atoms left in the excited state as well as on the energy density of the
incident radiation.
5. In stimulated emission of radiation an amplified beam is achieved while in
spontaneous emission there is no such amplification.
6. The light emitted through the spontaneous emission is not monochromatic while
in stimulated transition monochromatic radiation is obtained.
7. Spontaneous emission is not controllable from outside while stimulated emission is
controllable from outside.
8. In spontaneous emission, the net intensity is proportional to the number of
radiating atoms while in stimulated emission it is proportional to the square of the
number of radiation atoms.
Angle of Acceptance → If incident angle of light on the core for which the incident angle on the core-cladding interface equals the critical angle then incident angle of light on the core is called the "Angle of Acceptance. Transmission of light when the incident angle is equal to the acceptance angle If the incident angle is greater than the acceptance angle i.e. $\theta_{i}>\theta_{0}$ then the angle of incidence on the core-cladding interface will be less than the critical angle due to which part of the incident light is transmitted into cladding as shown in the figure below Transmission of light when the incident angle is greater than the acceptance angle If the incident angle is less than the acceptance angle i.e. $\theta_{i}<\theta_{0}$ then the angle of incidence on the core-cladding interface will be greater than the critical angle for which total internal reflection takes place inside the core. As shown in the figure below Transmission of lig
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