Spectroscopy is the study of light through light-matter interactions.
There are three main types of interactions:
- Quantized interactions in which involved molecules (Here: atoms, full or parts of molecules or crystals,..) jump from a stationary state to another stationary state. It is the most usual spectroscopy.
- Coherent interactions in which the involved molecules are excited to a non-stationary state during the interaction and return to their initial state. A detectable effect requires the coherence, that is the relations between the molecular parameters allowing the interaction (oscillating dipoles...) and the local electromagnetic fields are the same for all molecules.
- Mixed interactions: coherent and involving transitions of some molecules; example : He-Ne lasers.
Except refraction which is widely used, the coherent interactions are generally studied using lasers, so that, due to the intensity of these sources, the effects depend non-linearly on the intensity of the lasers. Some interactions require an intensity threshold.
Famous quotes containing the word coherent:
“We have good reason to believe that memories of early childhood do not persist in consciousness because of the absence or fragmentary character of language covering this period. Words serve as fixatives for mental images. . . . Even at the end of the second year of life when word tags exist for a number of objects in the child’s life, these words are discrete and do not yet bind together the parts of an experience or organize them in a way that can produce a coherent memory.”
—Selma H. Fraiberg (20th century)