page_title: Raman cooling
section_title: Two photon Raman process
hierarchical_section_title: Raman cooling / Two photon Raman process
caption_attribution_description: English: Figure showing a Raman two photon process between two states through a virtual state slightly red-detuned from a real excited state
context_page_description: In atomic physics, Raman cooling is a sub-recoil cooling technique that allows the cooling of atoms using optical methods below the limitations of Doppler cooling, Doppler cooling being limited by the recoil energy of a photon given to an atom. This scheme can be performed in simple optical molasses or in molasses where an optical lattice has been superimposed, which are called respectively free space Raman cooling and Raman side-band cooling. Both techniques make use of Raman scattering of laser light by the atoms.
context_section_description: The transition between two hyperfine states of the atom can be triggered by two laser beams: the first beam excites the atom to a virtual excited state (for example because its frequency is lower than the real transition frequency), and the second beam deexcites the atom to the other hyperfine level. The frequency difference of the two beams is exactly equal to the transition frequency between the two hyperfine levels.
  The illustration of this process is shown in the schematic illustration of a two-photon Raman process. It enables the transition between the two levels  and . The intermediate, virtual level is represented by the dashed line, and is red-detuned with respect to the real excited level, . The frequency difference  here matches exactly the energy difference between  and .
caption: Raman two photon process between two states through a virtual state slightly red-detuned from a real excited state
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