Adam, Gabrielle, Ben, and Jasmine
Important study questions concerning lasers:
1. How are photons created?
When atoms fall from a higher energy state to a lower one, energy is released. This energy is
released in the form of a photon. The photon is specific to the type of atom or molecule.
2. How is amplification accomplished?
Amplification occurs by one photon striking an excited atom or molecule and triggering the
release of an identical photon. This causes the presence of two identical photons. This process is also
known as stimulated emission. The excited atom travels back to the lower energy state when the
photon is released.
3. What population is inverted?
The population of ground state atoms or molecules to excited state atoms or molecules is
inverted. This causes the number of excited atoms or molecules to be greater than the number of
atoms in the ground state.
4. Why must a population be inverted?
If more molecules were in the ground state or lower energy level, then absorption would occur
instead of stimulated emission. This would kill the laser. The emitted photons would be absorbed by
the molecules allowing molecules to travel from the ground state to the excited state.
5. What does absorption have to do with the process?
Absorption would kill a laser. Absorption is the opposite of stimulated emission. If the
majority of the atoms or molecules were in the lower energy state, then the photons that were released
would be absorbed. The absorption process involves an atom using the photons energy to travel from
the ground state to a higher energy level. Without a population inversion, absorption would dominate
over stimulated emission.
6. What does pumping mean AND why is it important?
Pumping means to add energy to a sample of atoms or molecules, like electricity, to create a
population inverse. This addition of energy, pumping, causes more of the atoms to be in higher energy
state making the environment suitable for the formation of a laser.
7. How does stimulated emission compare to absorption?
Absorption and stimulated emission are inverse processes. Absorption takes an atom or
molecule from a lower state to a higher state while stimulated emission does exactly the opposite.
Absorption has exactly the same probability of occurring as does stimulated emission.
8. What is the difference between stimulated emission and spontaneous emission?
Spontaneous emission is when an atom just spontaneously releases a photon and travels from a
higher energy state to a lower energy state. Stimulated emission involves a previously formed photon
striking an excited atom or molecule. This action triggers the release of an identical photon, and the
excited molecule travels to a lower energy state. After stimulated emission two identical photons exist.
Spontaneous emission creates one photon.
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