PH2 definitions - photons, lasers etc.
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What is stimulated emission?
The emission of a photon from an excited atom.
Triggered by an incident photon of energy equal to the energy gap between the excited state and the lower energy state of the atom.
Emitted photon has same frequency, phase, direction of travel and polarisation as Incdent photon.
What is the critical angle?
When light approaches the boundary between two media from the 'slower' medium, the critical angle is the largest angle of incidence for which refraction can occur. The refracted wave is then travelling at 90° to the normal.
Define population inversion
A situation where a higher energy state in an atomic system is more heavily populated than a lower energy state (i.e. a less excited state or the ground state) of the same system.
What is pumping?
Feeding energy into the amplifying medium of a laser to produce a population inversion.
What is a lepton?
An electron or electron neutrino.
What are Hadrons?
Particles consisting only of quarks and antiquarks, (only quarks and antiquarks feel the strong force
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