Neodymium-doped Gain Media | previous | next | feedback |
You can buy neodymium-doped gain media from:
- EKSMA Optics offers various laser crystals including Nd:YAG and Nd:KGW.
Ask RP Photonics for advice on how to select the crystal material and dimensions, where to buy, your detailed laser design, etc.
Definition: laser gain media containing laser-active neodymium ions
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 directly pumping into the upper laser level 4F3/2 with 869-nm light. 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. 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 cavity. 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.
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.
The most common neodymium-doped gain media are:
- Nd:YAG = Nd:Y3Al5O12 (yttrium aluminum garnet, → YAG lasers): the classical choice for 1064 nm, but also usable at 946 and 1319 nm (and a few other lines); isotropic; still very common particularly for high-power lasers and Q-switched lasers
- Nd:YVO4 (yttrium vanadate, → vanadate lasers) for 1064, 914 and 1342 nm: very high pump and laser cross sections and larger gain bandwidth, compared with Nd:YAG, hence particularly attractive for low-threshold lasers; also good properties for high-power operation with good beam quality (low dn / dT); birefringent
- Nd:YLF = Nd:YLiF4 (yttrium lithium fluoride → YLF lasers) for 1047 and 1053 nm: birefringent, long upper-state lifetime, weak thermal lensing; useful for, e.g., high-power Q-switched lasers
- Nd:glass: various glasses, mostly silicates and phosphates; often used for neodymium-doped optical fibers, e.g. in fiber lasers and amplifiers (→ laser crystals versus glasses)
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. The latter 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, so that the power efficiency is not necessarily better than for neodymium-doped media.
Bibliography
| [1] | J. R. O'Connor, “Unusual crystal-field energy levels and efficient laser properties of YVO4:Nd”, Appl. Phys. Lett. 9, 407 (1966) |
| [2] | M. Ross, “YAG laser operation by semiconductor laser pumping”, Proc. IEEE 56, 196 (1968) |
| [3] | G. A. Massey, “Measurement of device parameters for Nd:YAlO3 lasers”, IEEE J. Quantum Electron. 8 (7), 669 (1972) |
| [4] | R. W. Waynant and P. H. Klein, “Vacuum ultraviolet laser emission from Nd3+:LaF3”, Appl. Phys. Lett. 46, 14 (1985) |
| [5] | T. Y. Fan et al., “Nd:MgO:LiNbO3 spectroscopy and laser devices”, J. Opt. Soc. Am. B 3 (1), 140 (1986) |
| [6] | A. I. Zagumennyi et al., “The Nd3+:GdVO4 crystal: a new material for diode-pumped lasers”, Sov. J. Quantum Electron. 22, 1071 (1992) |
| [7] | 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) |
| [8] | 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) |
| [9] | J. L. Blows et al., “Heat generation in Nd:YVO4 with and without laser action”, IEEE Photon. Technol. Lett. 10 (12), 1727 (1998) |
| [10] | N. Hodgson et al., “High power TEM00 mode operation of diode-pumped solid-state lasers”, Proc. SPIE 3611, 119 (1999) |
| [11] | 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) |
| [12] | 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) |
| [13] | 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) |
| [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 2: passively mode-locked operation”, Appl. Phys. B 92, 175 (2008) |
See also: gain media, rare-earth-doped gain media, ytterbium-doped gain media, YAG lasers, YLF lasers, vanadate lasers, tungstate lasers
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