RP Photonics

Encyclopedia … combined with a great Buyer's Guide!


Optical Refrigeration

Definition: a technique for cooling macroscopic samples via laser-induced fluorescence

German: optische Kühlung

Categories: methods, quantum optics

How to cite the article; suggest additional literature

Optical refrigeration (also called laser refrigeration or anti-Stokes fluorescent cooling) is a technique for cooling a macroscopic crystal (or a piece of glass) with a laser beam. The crystal must be doped, e.g. with ytterbium or thulium ions, which are excited by the laser beam. The laser wavelength is chosen such that it is longer than the average wavelength of the resulting fluorescence. This means that the energy of the absorbed photons is lower than the average energy of the emitted photons, so that energy is removed from the crystal. Of course, it is essential that the quantum efficiency of the fluorescence is high, and that nearly all fluorescence light can leave the crystal without being absorbed, e.g. by impurities: a single absorbed photon would offset the cooling effect of many other photons.

Cooling a piece of ZBLAN glass in a “laser fridge” from room temperature down to 208 K has been demonstrated [2], and 110 K have been achieved with Yb:LiYF4 (Yb:YLF) [7]. In theory, even temperatures of the order of 77 K (liquid nitrogen) should be reachable. Certain ytterbium-doped crystal materials, particularly tungstates such as Yb:KGW = Yb:KGd(WO4)2, appear to be suitable for this purpose.

Possible applications of laser refrigeration are the replacement of Stirling coolers and the like (avoiding moving parts, vibrations, etc.), but also radiation-balanced lasers, where the internal heat generation is essentially compensated by optical refrigeration.

It is instructive to consider entropy changes associated with laser refrigeration. The reduction in thermal entropy of the cooled device is more than compensated by the increase in entropy which arises from the conversion of narrow-band focused laser light into fluorescence light, which has a much higher entropy due to the many spatial modes and different frequencies involved in the emission.

See also the article on laser cooling, which deals with the cooling of microscopic particles, rather than macroscopic samples. The physical principles behind such cooling methods are rather different from those of optical refrigeration.


[1]P. Pringsheim, “Zwei Bemerkungen über den Unterschied von Lumineszenz und Temperaturstrahlung”, Z. Phys. 57, 739 (1929)
[2]R. I. Epstein et al., “Observation of laser-induced fluorescent cooling of a solid”, Nature 377, 500 (1995)
[3]S. R. Bowman and C. E. Mungan, “New materials for optical cooling”, Appl. Phys. B 71, 807 (2000)
[4]J. Thiede et al., “Cooling to 208 K by optical refrigeration”, Appl. Phys. Lett. 86, 154107 (2005)
[5]M. Sheik-Bahae and R. I. Epstein, “Optical refrigeration”, Nature Photon. 1, 693 (2007)
[6]D. V. Seletskiy, “Laser cooling of solids to cryogenic temperatures”, Nature Photon. 4 (3), 161 (2010)
[7]D. V. Seletskiy et al., “Local laser cooling of Yb:YLF to 110 K”, Opt. Express 19 (19), 18229 (2011)

(Suggest additional literature!)

See also: fluorescence, laser cooling, quantum efficiency, radiation-balanced lasers
and other articles in the categories methods, quantum optics

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media: