A portion of incident illumination on a sample is converted to charge carrier energy or into mechanical energy. Both of these conversions involve the pushing and pulling, i.e., accelerating and decelerating of net charges by the oscillating electric and magnetic fields of the incident illumination. These conversions can involve individual charge carriers such as electrons, or the dipole moment of entire molecules. Sometimes, if the incident illumination frequency matches the resonant frequency of the charge carrier or molecule, these conversions are one-way, in the process known as 'Absorption'. For example, electrons excited into the conduction band to propagate electric current, or the mechanical vibration of a molecule being converted to internal heat. Sometimes, these conversions are two-way. For example, electrons are accelerated and decelerated, which results in a nearly instantaneous release or 'emission' of energy, e.g., conversion back to light energy. Some of these two-way conversion energies continue to propagate or 'scatter' within the sample to be absorbed again, some simply continue through the sample and exit out the other side, and some simply return back out of the sample.