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Neodymium-doped Laser Gain Media

Author: the photonics expert

Definition: laser gain media containing laser-active neodymium ions

More general term: solid-state laser gain media

Categories: article belongs to category optical materials optical materials, article belongs to category laser devices and laser physics laser devices and laser physics

DOI: 10.61835/xxh   Cite the article: BibTex plain textHTML   Link to this page   LinkedIn

Neodymium (chemical symbol: Nd) is a chemical element belonging to the group of rare earth metals. In laser technology, it is widely used in the form of the trivalent ion Nd3+ as the laser-active dopant of gain media based on various host materials, including both crystals and glasses.

The usual pump wavelength is 808 nm (for Nd:YAG; wavelengths for other host materials can somewhat differ), but a higher slope efficiency can be achieved by direct pumping into the upper laser level 4F3/2 with 869-nm light (which is sometimes called in-band pumping, although this is inaccurate). The strongest laser transition is that from 4F3/2 to 4I11/2 for 1064 nm, but other transitions are available with longer or shorter wavelengths (see Figure 1). In order to achieve lasing on those, lasing at the 1064-nm line needs to be suppressed by inserting an appropriate wavelength filter (usually consisting of one or more dichroic mirrors) into the laser resonator. Via multi-phonon emission, the populations in levels 4I11/2 to 4I15/2 are quickly transferred to the ground-state manifold 4I9/2. (The lower-state lifetime is much smaller than the upper-state lifetime.) Hence, there is normally negligible population in all these levels, so that neodymium-doped gain media exhibit pure four-level behavior. The exception is the case where the lower level is the ground-state manifold 4I9/2: 946-nm Nd:YAG lasers (and other Nd-based lasers emitting between 900 and 1000 nm) are quasi-three-level lasers, exhibiting a fairly high threshold pump power.

energy level structure of the trivalent neodymium ion in Nd^{3+}:YAG
Figure 1: Energy level structure of the trivalent neodymium ion (with wavelength numbers for Nd:YAG).

For high excitation densities, as can occur particularly in Q-switched lasers, but also in lasers operating on the weaker laser transitions, there can be significant energy losses due to energy transfer (→ upconversion) to higher-lying levels with small lifetimes.

Overview on Neodymium-doped Gain Media

The most common neodymium-doped gain media are:

Less common neodymium-doped gain media are:

  • Nd:GdVO4 (gadolinium vanadate) for 1064 and 1341 nm: similar to Nd:YVO4, but having a larger gain bandwidth
  • Nd:GDD (gadolinium gallium garnet): used for high-power heat capacity lasers
  • the tungstates Nd:KGW = Nd:KGd(WO4)2 and Nd:KYW = Nd:KY(WO4)2: birefringent, large gain bandwidth, large Raman cross-sections
  • Nd:YALO = Nd:YAlO3 for 1079 and 930 nm: birefringent
  • Nd:YAP = Nd:YAlO3 for 1079 or 1340 nm: high thermal conductivity, birefringent
  • Nd:LSB = Nd:LaSc3(BO3)4 for 1062, 905 and 1348 nm: birefringent; allows very high neodymium concentration
  • Nd:S-FAP = Nd:Sr5(PO4)3F for 1059, 923 and 1328 nm: birefringent

In all these media (except for some glasses), the neodymium dopant ions replace other ions (often yttrium) of the host medium which have about the same size.

Neodymium-doped gain media face competition from ytterbium-doped media in the 1-μm spectral region. Those have a smaller quantum defect, usually a higher emission bandwidth and a higher upper-state lifetime, also a simpler energy level structure which avoids various quenching processes. However, they exhibit quasi-three-level behavior, which tends to lead to a higher threshold pump power, so that the power efficiency is not necessarily better than for neodymium-doped media.

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Bibliography

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[2]M. Ross, “YAG laser operation by semiconductor laser pumping”, Proc. IEEE 56, 196 (1968); https://doi.org/10.1109/PROC.1968.6220
[3]J. R. Thornton et al., “Properties of neodymium laser materials”, Appl. Opt. 8 (6), 1087 (1969); https://doi.org/10.1364/AO.8.001087
[4]G. A. Massey, “Measurements of device parameters for Nd:YAlO3 lasers”, IEEE J. Quantum Electron. 8 (7), 669 (1972); https://doi.org/10.1109/JQE.1972.1077254
[5]R. W. Waynant and P. H. Klein, “Vacuum ultraviolet laser emission from Nd3+:LaF3”, Appl. Phys. Lett. 46, 14 (1985); https://doi.org/10.1063/1.95833
[6]T. Y. Fan et al., “Nd:MgO:LiNbO3 spectroscopy and laser devices”, J. Opt. Soc. Am. B 3 (1), 140 (1986); https://doi.org/10.1364/JOSAB.3.000140
[7]A. I. Zagumennyi et al., “The Nd3+:GdVO4 crystal: a new material for diode-pumped lasers”, Sov. J. Quantum Electron. 22, 1071 (1992); https://doi.org/10.1070/QE1992v022n12ABEH003672
[8]S. Kück et al., “Excited state absorption and stimulated emission of Nd3+ in crystals. Part 1: Y3Al5O12, YAlO3, and Y2O3”, Appl. Phys. B 67 (2), 151 (1998); https://doi.org/10.1007/s003400050486
[9]L. Fornasiero et al., “Excited state absorption and stimulated emission of Nd3+ in crystals. Part 2: YVO4, GdVO4, and Sr5(PO4)3F”, Appl. Phys. B 67, 549 (1998); https://doi.org/10.1007/s003400050543
[10]J. L. Blows et al., “Heat generation in Nd:YVO4 with and without laser action”, IEEE Photon. Technol. Lett. 10 (12), 1727 (1998); https://doi.org/10.1109/68.730483
[11]N. Hodgson et al., “High power TEM00 mode operation of diode-pumped solid-state lasers”, Proc. SPIE 3611, 119 (1999); https://doi.org/10.1117/12.349265
[12]L. Fornasiero et al., “Excited state absorption and stimulated emission of Nd3+ in crystals III: LaSc3(BO3)4, CaWO4, and YLiF4”, Appl. Phys. B 68, 67 (1999); https://doi.org/10.1007/s003400050587
[13]Y. Sato and T. Taira, “The studies of thermal conductivity in GdVO4, YVO4, and Y3Al5O12 measured by quasi-onedimensional flash method”, Opt. Express 14 (22), 10528 (2006); https://doi.org/10.1364/OE.14.010528
[14]D. Krennrich et al., “A comprehensive study of Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:YGdVO4 lasers operating at wavelengths of 0.9 and 1.3 μm. Part 1: cw-operation”, Appl. Phys. B 92, 165 (2008); https://doi.org/10.1007/s00340-008-3069-4
[15]D. Krennrich et al., “A comprehensive study of Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:YGdVO4 lasers operating at wavelengths of 0.9 and 1.3 μm. Part 2: passively mode-locked operation”, Appl. Phys. B 92, 175 (2008); https://doi.org/10.1007/s00340-008-3070-y

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