Laser
Stimulated (induced) EmissionSpontaneous Emission vs Stimulated emission
Spontaneous (Self) Emission
Population inversion
How laser worksEnergy Distribution
2. Pumping
3. Optical resonator1.
Amplifying/active medium
Emission and Absorption – Basic ideas
Three basic processes
Eins...
Laser
Light Amplification by Stimulated Emission of Radiation
The laser is a device that produces coherent ( All waves are exactly in phase with
one another) nearly monochromatic, Less diverging and extremely intense beam
optical radiation by stimulating electronic/ionic/molecular transitions to higher
energy levels when they return to lower energy levels by stimulated emission, they
emit energy.
Laser light Ordinary light
Stimulated emission Spontaneous emission
Monochromatic Poly/monochromatic
Highly energized Poorly energized
Directional Highly diverging
Coherent Non-coherent
Can be focused sharply Difficult to be focused sharply
Even 2022 PH 212 (Modern Physics) 3
, Absorption (Stimulated)
In this process a photon with an energy equals
to the difference in energy between two of the
atomic levels interacts with the atom. The
electron of the atom is in the lower energy
state, absorbs the photon, and jumps to the
higher energy state (excited state). The photon
is completely absorbed by the atom. The final
state of the atom is excited.
Energy is absorbed by an atom, the electrons are excited into vacant energy shells.
Even 2022 PH 212 (Modern Physics) 5
, Spontaneous (Self) Emission
In this case, one of the electron is not in the
lowest possible energy state; thus, the atom is
excited. Spontaneously, the atom emits a
photon with an energy equals to the difference
in energy between the energy when the
electron is in the excite state and the energy of
the level when the electron is in the relaxed
state (lower energy state). During this emission
the electron jumps down to the lower energy
state.
The atoms give up energy which is carried by the emitted photon and it is left
unexcited. On the other side, the emitted photon has an energy equals to the
difference in energy between the two atomic states involved. However, there is not
a prefer direction of motion for the emitted photon; in fact, the direction of
emission is completely random.
Atoms in an upper energy level can be triggered or stimulated in phase by an incoming
photon of a specific energy.
Even 2022 PH 212 (Modern Physics) 6
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