This is the distance along the propagation direction of a beam from the waist to the place where the area of the cross section is doubled. An associated variable is the confocal parameter, b, which is twice the Rayleigh range.
This is a measure of how fast the beam diverges far from the beam waist. A laser light with a narrow beam divergence is mostly used to make laser pointer devices. Normally the beam divergence of laser light is measured using beam profiler.
Brewsters angle is an angle of incidence at which light with a specific polarization is perfectly transmitted via a transparent dielectric surface, with no reflection. When unpolarized beam is incident at this angle, the light that is reflected from the surface is thus seamlessly polarized.
Spontaneous emission refers to the process by which a light source like an atom, molecule in an excited state undergoes a transition to a state with a lower energy for instance the ground state and emits a photon.
Depending on the nature of the indeterminacy, there are two mechanism of broadening. If the indeterminacy in the frequency or wavelength is due to a phenomenon that is the same for each quantum emitter, there is homogeneous broadening, while if each quantum emitter has a different type of fluctuation, the broadening is inhomogeneous.
The most often cases in solid state systems where the fluctuation differs for each system (inhomogeneous broadening) is when as a result of the presence of dopants, the local electric field is different for each emitter, and so the stark effect changes the energy levels in an inhomogeneous way. The homogeneous broadened emission line will have a Lorentzian profile whereas the in homogeneously broadened emission will have a Gaussian profile. One phenomena may be present at the same time, however if one has a broader fluctuation, it will be the one responsible for