The Raman laser is a byproduct of Raman scattering, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan in liquids and independently by Grigory Landsberg and Leonid Mandelshtam in crystals. When light hits a substance, it causes the atoms in the substance to vibrate sympathetically. The collision of photons with the substance causes some of the photons to gain or lose energy, resulting in a secondary light of a different wavelength. A Raman laser takes this secondary light and amplifies it by reflecting it and pumping energy into the system to emit a coherent laser beam. The most significant difference between a Raman laser and a standard laser is the absence of population inversion in a Raman laser.
In 2002, researchers at UCLA demonstrated Raman light transmission from optical wires on a silicon quantum chip and in 2004 they demonstrated the first silicon laser. In February 2005, researchers at Intel demonstrated the second generation of such lasers that are capable of operating in continuous-mode on silicon chips. It is expected that these breakthroughs will greatly reduce the cost of optical computing and communications devices by 2010. Because of its crystalline structure, silicon atoms readily vibrate when hit with light. The Raman effect is 10,000 times stronger in silicon than in glass.
In 2007, researchers at JPL/Caltech have also discovered Raman lasing with fluorite resonators, demonstrating record low threshold and high efficiency.
The Raman effect can lead to higher energy photon emission, or, more commonly, to lower energy photon emission.