As optical pumping refers to a physical effect of a population inversion by optical excitation ( electron - photon causes interaction). A population inversion occurs when the energy levels of a particle are not so populated with electrons as would be expected without optical excitation according to the given temperature. The technique was developed by Alfred Kastler ( Nobel Prize 1966) in the early 1950s.
Various properties of the system consisting of the energy level and the excitation system influence the "pumpability" of a level. These are:
- Temperature of the system, and thus occupation of the levels according to the Boltzmann distribution
- Excitation rate
- Lifetime of the states in the excited level
- possibly the lifespan of the states of the energy levels over which the pumped level empties
In laser optical pumping (eg. Dyes, crystals) is the first step in which the optically active medium in the resonator by an external energy source (eg. As other lasers, flashlamp) is stimulated, ie electrons in the case of a higher energy level can be "raised" ( optical resonance ). Technical lasers are usually operated at room temperatures, so the critical prerequisite for optical pumping is the existence of long-lasting energy levels, either in the pumped level or in the indirectly filled levels.
The mechanisms on which optical pumping is based are used, in addition to their technical use in lasers, in certain resonance spectroscopy studies . By cooling the samples to be examined and using high excitation rates, “non-equilibrium populations can be created” in a large number of systems and these can be excited to luminescence .
Since energy levels can also be influenced by additional field effects (static magnetic fields, static electric fields), the luminescence of the pumped levels can be used to:
- Determine properties of pumped levels
- Analyze transfer processes to other levels
If alternating fields are also used, optically pumped levels can also be emptied via additional resonance effects (e.g. microwave resonance). This leads to so-called multi-resonance measurement methods (e.g. optically proven magnetic resonance - ODMR).
- Arnold L. Bloom: Optical pumping. In: Scientific American. vol 203, October 1960.
- Thomas R. Carver: Optical pumping. In: Science. vol 141, August 1963.
- Robert L. De Zafra: Optical pumping. In: American Journal of Physics. 1960.