Neodymium-doped Laser Gain Media
Author: the photonics expert Dr. Rüdiger Paschotta
Definition: laser gain media containing laser-active neodymium ions
More general term: solid-state laser gain media
Categories: optical materials, 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.
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:
- 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 <$\partial n / \partial T$>); 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 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. 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.
More to Learn
Encyclopedia articles:
- laser gain media
- rare-earth-doped laser gain media
- rare-earth-doped fibers
- laser crystals
- ytterbium-doped laser gain media
Suppliers
The RP Photonics Buyer's Guide contains 58 suppliers for neodymium-doped laser gain media. Among them:
Fibercore
Fibercore has delivered over 40 years of innovation and excellence in developing and manufacturing speciality optical fiber. All of our fiber products have been developed with our customers in mind with market leading capabilities to produce an extensive range of fibers including;
- single-mode (SM) fiber
- doped fiber
- polarization-maintaining (PM) fiber
- multimode (MM) fiber
- multicore fiber
- spun HiBi fiber
We are continuously expanding our product ranges to cover wider and more demanding customer applications. So if you have a specific development project or require a custom fiber, we would like to discuss it further with you. We will work together with you to find the best solution.
Optogama
Optogama offers various types of neodymium-doped laser crystals:
- Nd:KGW crystals exhibit strong and broad absorption and emission bands without significant luminescence quenching even for high doping concentrations. Optogama offers Nd:KGW crystals for medium-power but highly efficient continuous-wave (CW), Q-switched and mode-locked lasers with diode-laser and flashlamp pumping. In addition, it is possible to use Nd:KGW crystal for efficient self-Raman conversion.
- Nd:YLF is characterized by a long lifetime of the 4F3/2 upper laser level. Compared to Nd:YAG, the negative dn/dT leads to lower thermal distortions and thus to a better output beam quality. Another distinctive feature is high UV transparency, which is favorable for pumping with xenon flashlamps.
Laserton
Laserton has neodymium-doped laser crystals, specifically Nd:YAG and Nd:YVO4.
Exail
Exail (formerly iXblue) offers a complete range of neodymium-doped fibers with some unique properties, ideal for fiber lasers between 890 and 1100 nm.
Exail neodymium aluminosilicate double clad fibers have been developed to maximize fiber efficiency through a precisely controlled host composition. Compared to a standard neodymium-doped fiber, the 1.06-μm emission is reduced through careful fiber design optimization. Our double clad fibers are routinely tested to various parameters such as photodarkening and environmental behavior.
Single clad fibers are also proposed and would be ideal to build seeder sources.
Benefits and features:
- host composition optimized for high energy efficiency and low clustering
- high NA, high performance low-index cladding
- low splicing losses, low background losses, low macrobending losses at the operating wavelength
Applications: 0.9 to 1.064-μm fiber lasers, seeder sources at 10xx nm.
Shalom EO
Shalom EO offers Nd:YAG, Nd:Ce:YAG and Nd:YVO4 laser crystals for solid-state lasers.
EKSMA OPTICS
EKSMA Optics has high optical quality Nd:YAG laser crystals – rods with high damage threshold AR@1064 nm coatings. Custom Nd:YAG rods can be manufactured on request.
Bibliography
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[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 |
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This encyclopedia is authored by Dr. Rüdiger Paschotta, the founder and executive of RP Photonics AG. How about a tailored training course from this distinguished expert at your location? Contact RP Photonics to find out how his technical consulting services (e.g. product designs, problem solving, independent evaluations, training) and software could become very valuable for your business!
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