Erbium-doped Laser Gain Media
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: laser gain media doped with erbium ions
More general term: solid-state laser gain media
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DOI: 10.61835/6ml Cite the article: BibTex plain textHTML Link to this page! LinkedIn
Erbium (chemical symbol: Er) is a chemical element belonging to the group of rare earth metals. It is widely used in the form of the trivalent ion Er3+ as the laser-active dopant of gain media based on various host materials, including both crystals and glasses.
Erbium-doped Glasses
Erbium-doped glasses, mostly of silicate and phosphate types, are used both for bulk lasers and fiber lasers and amplifiers. The most common laser transition (also widely used in erbium-doped fiber amplifiers) is that from the 4I13/2 manifold to the ground-state manifold 4I15/2 (Figure 1). Depending on the glass composition, the transition wavelength is usually somewhere between 1.53 and 1.6 μm. Because that transition is a quasi-three-level transition, erbium-doped laser and amplifiers require a significant fractional excitation of the erbium ions, and erbium lasers typically exhibit a high threshold pump power.
The most common pump scheme is based on the transition 4I15/2 → 4I11/2 with a wavelength around 0.9–1 μm, although in-band pumping (4I15/2 → 4I13/2, e.g. at 1.45 μm) is also possible. A multi-phonon transition, which is relatively fast in silicate glasses (due to their high phonon energies), leads from 4I11/2 to 4I13/2. The upper-state lifetime of 4I13/2 is of the order of 8–10 ms, whereas all higher-lying levels have lifetimes of at most a few microseconds due to fast multi-phonon decay.
Particularly in bulk crystals, but also in fibers, efficient pump absorption on the 4I15/2 → 4I11/2 transition is difficult to achieve because the absorption cross-sections are relatively small, and the doping concentration is limited by the need to avoid excessive quenching processes. A common method to solve this problem is codoping with ytterbium (Yb3+) sensitizer ions, which leads to an erbium-ytterbium-doped laser gain medium. The ytterbium ions can efficiently absorb pump radiation e.g. at 980 nm, and then transfer the energy to erbium ions in the ground-state manifold, bringing them into 4I11/2. From that level, the ions are quickly transferred into the upper laser level 4I13/2, so that energy transfer back to ytterbium is suppressed. Erbium–ytterbium-doped fibers are used e.g. for erbium-doped fiber amplifiers and for short fiber lasers.
The behavior of Er3+ ions is substantially different in some host glasses (e.g. fluoride glasses) with a lower phonon energy, which strongly reduces multi-phonon transition rates. In such glasses, a variety of higher-lying energy levels can be populated, and a number of different pumping and lasing schemes are possible. For example, it is possible to realize green-emitting upconversion fiber lasers [2], or lasers emitting around 2.9 μm [12].
In addition to the mentioned optical and multi-phonon transitions, many energy transfer processes can occur, particularly for high doping concentrations. For example, cooperative upconversion can occur, where one erbium ion in 4I13/2 transfers energy to a second ion in that level, resulting in one ion in 4I9/2 and another one in the ground-state manifold. Due to the multitude of excited levels, and also because of the different behavior of ions in clusters, it is difficult to obtain reliable spectroscopic data for comprehensive modeling of such processes.
Erbium-doped bulk glasses are used e.g. for Q-switched lasers (e.g. as eye-safe microchip lasers) emitting in the 1.5-μm spectral region, as are applied e.g. for range finding. Such glasses can also be pumped with flash lamps, particularly when the absorption efficiency is increased, e.g. with chromium (Cr3+) or ytterbium (Yb3+) codopants. (Such codopants can absorb additional energy from the pump light and partially transfer it to erbium ions.) The main application of erbium-doped glasses, however, is in erbium-doped fiber amplifiers for optical fiber communications.
Erbium-doped Crystals
Lasing of erbium ions was first realized with highly doped Er:YAG crystals [1]. In that case, the laser transition is 4I11/2 → 4I13/2, with an emission wavelength around 2.9 μm. For low doping concentrations, this laser transition would be self-terminating, as the lower level has a significantly longer lifetime than the upper level. For high erbium concentrations, however, complicated energy transfer processes changes this situation.
Er:YAG lasers can also be operated on the 4I13/2 → 4I15/2 transition, then emitting around 1.645 μm. Efficient operation can be achieved by in-band pumping e.g. with an erbium-doped fiber laser emitting at 1.53 μm.
Er:YAG crystals can be pumped with flash lamps or (much more efficiently) with laser diodes. They are often used in Q-switched lasers. The 2.9-μm light is strongly absorbed in water, making such lasers suitable for a variety of medical applications.
Erbium is also sometimes used in other laser crystals, such as Er:YLF, Er:YALO, tungstates and vanadates.
Related Articles
| Laser gain media |
| Erbium-ytterbium-doped laser gain media |
| Rare-earth-doped laser gain media |
| Quasi-three-level laser gain media |
| Upconversion lasers |
Suppliers
The RP Photonics Buyer's Guide contains 34 suppliers for erbium-doped laser gain media. Among them:
Fibercore
Fibercore's portfolio of erbium-doped fiber, PM erbium fiber, dual-clad erbium/ytterbium-doped fiber, triple-clad doped fiber and other doped fibers offers ideal suitability for high-power erbium-doped fiber amplifiers (EDFAs) and fiber lasers.
Exail
The amplification of optical transmission signals is enabled through our high efficiency erbium-doped fibers (ideal for C and L band amplifiers). Our wide range of erbium-doped optical fibers allows for tailored optical amplifiers (EDFAs) performance based on your requirements. Exail’s erbium-doped fiber (EDF) products have been optimized to fulfill the exigency of high efficiency and low noise EDFAs in the C & L bands. They cover a wide range of applications, from telecom to LIDAR. Space radiation versions are available (TRL 9).
Benefits & features:
- low noise figure
- flat gain shape
- high efficiency
- low splice loss
- highly consistent spectroscopic data
- 80 µm reduced cladding on request
- PM Panda structure
Applications: 1.5-μm lasers and amplifiers, EDFAs, fiber lasers, small footprint fiber amplifiers.
Le Verre Fluore
Thanks to their high rare-earth solubility (up to 100,000 ppm) and low phonon energy, LVF fluoride fibers offer dozens of active transitions, enabling a broad range of applications from visible to the mid-infrared.
LVF erbium-doped fibers are available as single-mode fibers or double cladding fibers.
LVF erbium doped fibers can be used for laser emission at visible wavelengths (470 nm, 540 nm), infrared wavelengths (1.55 µm) and mid-infrared wavelengths (2.94 µm, 3.5 µm).
Optogama
Optogama offers a range of high-quality erbium-doped laser gain media, ideal for eye-safe applications around 1.5 µm. These materials are optimized for diode-pumped solid-state lasers used in telecommunications, LIDAR, rangefinding, and medical systems.
We supply both phosphate and crystalline hosts co-doped with ytterbium to enhance pump efficiency and energy storage. Our crystals are precisely fabricated to deliver excellent thermal handling, optical homogeneity, and long operational lifetimes.
Megawatt Lasers
MegaWatt Lasers Inc. has a large inventory laser rods, including Er:YAG rods. We also can assist in the design and modeling for various applications.
Bibliography
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