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Energy Transfer

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Definition: the phenomenon that dopant ions in laser-active media can exchange excitation energy among each other

German: Energietransport

Category: physical foundations

How to cite the article; suggest additional literature

Particularly in highly doped solid-state gain media (laser crystals, glasses, and rare-earth-doped fibers), energy transfer between different dopant ions can occur. The dominant mechanism behind this is usually the dipole–dipole resonant interaction (Förster energy transfer) between closely located ions, rather than emission and reabsorption of fluorescence photons, although the latter mechanism can be significant over longer distances. As the strength of the dipole–dipole interaction rapidly vanishes with increasing distance between the ions (with the inverse sixth power of distance), its overall importance depends strongly on the doping concentration, the size of the crystal's unit cell and also the tendency of ions to form clusters.

If the energy loss of the “giving” ion (the donor) is larger than the energy gain of the “receiving” (acceptor) ion, the excess energy can be taken away by one or several phonons. One is then dealing with (multi-)phonon-assisted energy transfers.

There are other kinds of energy transfer processes, occurring e.g. between molecules in liquids (and possibly involving the exchange of electrons) or between colliding atoms or molecules in gases.

The strength of energy transfer processes can be quantified with energy transfer parameters in rate equation models. The rate of a particular energy transfer process is then normally described as the product of such a parameter and the excitation densities of the involved electronic levels.

Effects of Energy Transfers

The main effects of energy transfers in laser gain media are:

energy transfer

Figure 1: Energy transfer between ions of the same species.

energy transfer from Yb to Er

Figure 2: Energy transfer from Yb3+ to Er3+.

cross relaxation by energy transfer

Figure 3: Cross relaxation of two ions.

Auger upconversion

Figure 4: Cooperative (Auger) upconversion.

Bibliography

 [1]E. Snitzer and R. Woodcock, “Yb3+–Er3+ glass laser”, Appl. Phys. Lett. 6, 45 (1965)
[2]K. Arai et al., “Aluminium or phosphorus co-doping effects on the fluorescence and structural properties of neodymium-doped silica glass”, J. Appl. Phys. 59 (10), 3430 (1986)
[3]R. Wyatt, “Spectroscopy of rare earth doped fibres”, Proc. SPIE 1171, 54 (1989)
 [4]J. E. Townsend et al., “Yb3+ sensitized Er3+ doped silica optical fiber with ultrahigh transfer efficiency and gain”, Electron. Lett. 27, 1958 (1991)
 [5]J. Y. Allain et al., “Energy transfer in Pr3+/Yb3+-doped ZBLAN fibres and application to lasing at 2.7 μm”, Electron. Lett. 27, 1012 (1991)
[6]S. Taccheo et al., “Measurement of the energy transfer and upconversion constants in Er–Yb-doped phosphate glass”, Opt. Quantum Electron. 31, 249 (1999)
[7]P. J. Hardman et al., “Energy-transfer upconversion and thermal lensing in high-power end-pumped Nd:YLF laser crystals”, IEEE J. Quantum Electron. 35 (4), 647 (1999)
[8]J. F. Philipps et al., “Energy transfer and upconversion in erbium–ytterbium-doped fluoride phosphate glasses”, Appl. Phys. B 74 (3), 233 (2002)
[9]M. Laroche et al., “Accurate efficiency evaluation of energy-transfer processes in phosphosilicate Er3+-Yb3+-doped fibers”, J. Opt. Soc. Am. B 23 (2), 195 (2006)

(Suggest additional literature!)

See also: gain media, upconversion, quenching, clustering, spatial hole burning, rate equation modeling, non-radiative transitions
and other articles in the category physical foundations

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