Population Gratings: The writing lasers are resonant with optical transitions in the matter and the grating is formed by optical pumping.
Strain splits and shifts optical transitions from individual centers resulting in broad lines in the ensembles of centers.
Thus optical transitions must preserve the total spin and occur between levels of the same total spin.
Therefore, already the Coulomb interaction among produces a new solid-state effect compared with optical transitions in simple atoms.
For interband optical transitions, carriers change momentum through a slow, intermediate scattering process, dramatically reducing the optical emission intensity.
G. Dorfman in 1923 when he suggested that the optical transitions due to Zeeman splitting could provide a way to study ferromagnetic structure.
They are, however, only well suited for systems with optical transitions between isolated levels in which many-body interactions are of minor importance as is sometimes the case in atoms or small molecules.
It is well known the optical transition of electrons and holes in the solid state is a useful clue to understand the physical properties of the material.
There, the scintillation process is due to an optical transition of the Bi ion, a major constituent of the crystal.
By using lower frequencies than for optical transitions the Doppler broadening could be neglected (Doppler broadening is proportional to the frequency).
