An atomic system is characterized by discrete energy states, and usually the atoms exist in the lowest energy state, which is normally referred to as the ground state. An atom in a lower energy state may be excited to a higher energy state through a variety of processes. One of the important processes of excitation is through collisions with other particles. The excitation can also occur through the absorption of electromagnetic radiation of proper frequencies; such a process is known as stimulated absorption or simply as absorption. On the other hand, when the atom is in the excited state, it can make a transition to a lower energy state through the emission of electromagnetic radiation; however, in contrast to the absorption process, the emission process can occur in two different ways.
KeywordsSpontaneous Emission Stimulate Raman Scattering Population Inversion Laser Medium Lower Energy State
- Einstein, A. (1917), On the quantum theory of radiation, Phys. Z. 18, 121. (This paper has been reprinted in Laser Theory by F. S. Barnes, IEEE Press, New York, 1972.)Google Scholar
- Turitsyn, S. K., Ania-Castanon, J. D., Babin, S. A., Karalekas, V., Harper, P., Churkin, D., Kablukov, S. I., El-Taher, A. E., Podivilov, E. V., and Mezentsev, V. K. (2009), 270-km ultralong Raman fiber laser, Phys. Rev. Lett. 103, 133901-1.Google Scholar