Anti-Stokes cooling allows laser cooling to be applied to macroscopic samples. The idea for anti-Stokes cooling was first advanced by Pringsheim in 1929.[1] While Doppler cooling lowers the translational temperature of a sample, anti-Stokes cooling decreases the vibrational or phonon excitation of a medium. This is accomplished by pumping a substance with a laser beam from a low-lying energy state to a higher one with subsequent emission to an even lower-lying energy state. The principal condition for efficient cooling is that the anti-Stokes emission rate to the final state be significantly larger than that to other states as well as the nonradiative relaxation rate. Because vibrational or phonon energy can be many orders of magnitude larger than the energy associated with Doppler broadening, the efficiency of heat removal per laser photon expended for anti-Stokes cooling can be correspondingly larger than that for Doppler cooling.
The anti-Stokes cooling effect was first demonstrated by Djeu and Whitney in CO2 gas.[2] The first anti-Stokes cooling in a solid was demonstrated by Epstein et al. in 1995, in a ytterbium doped fluoride glass sample.[3] In 1999, Gosnell et al. cooled a fiber of ytterbium-doped fluoride glass (Yb:ZBLAN) to 236 K.[4] Subsequently in 2005, the same solid was further cooled to 208 K.[5] In 2010, cooling to a cryogenic temperature 155 K was achieved in a LiYF4 crystal.[6] In 2013, Melgaard et al. cooled Yb:YLF to 119 K.[7] The lowest temperature achieved by anti-Stokes cooling, 90 K, was demonstrated in 2017 by Gragossian et al. in Yb:YLF by using a multipass Herriott cell to compensate for the small absorption probability of the material by giving a photon many opportunities to be absorbed before leaving the experiment. [8]
Potential practical applications for anti-Stokes cooling of solids include radiation balanced solid state lasers and vibration-free optical refrigeration, useful in applications like space-based optics where cryogens would carry a significant weight and complexity penalty.[9][10]
References
edit- ^ P. Pringsheim (1929). Pringsheim, Peter (1929). "Zwei Bemerkungen über den Unterschied von Lumineszenz- und Temperaturstrahlung". Zeitschrift für Physik. Vol. 57, no. 11–12. pp. 739–746. doi:10.1007/BF01340652.
- ^ N. Djeu and W.T. Whitney (1981) Djeu, N.; Whitney, W. T. (1981). "Laser cooling by spontaneous anti-Stokes scattering". Physical Review Letters. Vol. 46, no. 4. pp. 236–239. doi:10.1103/PhysRevLett.46.236.
- ^ R.I. Epstein, M.I. Buchwald, B.C. Edwards, T.R. Gosnell, and C.E. Mungan (1995) "Observation of laser-induced fluorescent cooling of a solid". Nature.
- ^ Gosnell, T. (1999). "Laser cooling of a solid by 65 K starting from room temperature". Opt. Lett. 24 (15): 1041–1043. Bibcode:1999OptL...24.1041G. doi:10.1364/OL.24.001041. PMID 18073934.
- ^ Thiede, J. (2005). "Cooling to 208K by optical refrigeration". Applied Physics Letters. 86 (15). Bibcode:2005ApPhL..86o4107T. doi:10.1063/1.1900951.
- ^ Seletskiy, D. (2010). "Laser cooling of solids to cryogenic temperatures". Nature Photon. 4 (3): 161–164. Bibcode:2010NaPho...4..161S. doi:10.1038/nphoton.2009.269.
- ^ Seth, D. (2013). "Optical refrigeration to 119\&\#xA0;K, below National Institute of Standards and Technology cryogenic temperature". Opt. Lett. 38 (9): 1588–1590. doi:10.1364/OL.38.001588. PMID 23632561.
- ^ Gragossian, Aram (2017). "Optical refrigeration inches toward liquid-nitrogen temperatures". SPIE. doi:10.1117/2.1201704.006840.
- ^ S.R. Bowman (1999) Bowman, S.R. (1999). "Lasers without internal heat generation". IEEE Journal of Quantum Elect. Vol. 35. pp. 115–122. doi:10.1109/3.737628.
- ^ D.V. Seletskiy, R. Epstein, and M. Sheik-Bahae (2016) Seletskiy, Denis V.; Epstein, Richard; Sheik-Bahae, Mansoor (2016). "Laser cooling in solids: advances and prospects". Reports on Progress in Physics. Vol. 79, no. 9. p. 096401. doi:10.1088/0034-4885/79/9/096401.