RP Photonics logo
VL logo part of the
Virtual
Library

Encyclopedia of Laser Physics and Technology

Ytterbium-doped Gain Media

previous  |  next  |  feedback

You can buy ytterbium-doped gain media from:


Ask RP Photonics for advice on how to select the ytterbium-doped crystal material and dimensions, how to compare with neodymium, where to buy, your detailed laser design, etc.

Definition: laser gain media containing laser-active ytterbium ions

Ytterbium (chemical symbol: Yb) is a chemical element belonging to the group of rare-earth metals. In laser technology, it has acquired a prominent role in the form of the trivalent ion Yb3+, which is used as a laser-active dopant in a variety of host materials, including both crystals and glasses. It is often used for high-power lasers and for wavelength-tunable solid-state lasers.

Special Properties of Ytterbium-doped Gain Media

energy levels of ytterbium ions in Yb:YAG

Figure 1: Energy levels of Yb3+ ions in Yb:YAG, and the usual pump and laser transitions.

Ytterbium-doped laser crystals and glasses have a number of interesting properties, which differ from those e.g. of neodymium-doped gain media:

Quasi-three-level Characteristics

The small quantum defect also has a usually unwanted consequence: the significant quasi-three-level behavior, particularly at short wavelengths, which requires such lasers to be operated with relatively high pump intensities and makes it more difficult to fully realize the potential for high power efficiency. Another difficulty arises for the resonator designs of end-pumped ytterbium lasers: a resonator mirror for injecting the pump light must have a high reflectivity at the laser wavelength and a high transmission at the only slightly shorter pump wavelength. Dichroic mirrors with such properties for closely lying wavelengths are difficult to make.

cross sections of Yb-doped glass

Figure 2: Absorption and emission cross sections of ytterbium-doped germanosilicate glass, as used in the cores of ytterbium-doped fibers. (Data from spectroscopic measurements by R. Paschotta)

Figure 2 shows the ytterbium cross sections of a germanosilicate glass. Efficient pumping is possible around 910 nm wavelength, or near 975 nm. In the latter case, the pump linewidth must be small, and only ∼50% excitation level can be achieved due to stimulated emission, but the absorption length and the quantum defect are smaller. Strong three-level behavior occurs for lasing around 1030 nm, whereas nearly four-level behavior is observed beyond 1080 nm, where there is very little reabsorption. For ytterbium-doped crystals (e.g. Yb:YAG), there is often a choice between different lasing transitions, where typically those with shorter wavelengths exhibit more pronounced three-level characteristics.

Overview on Ytterbium-doped Gain Media

There is a very wide range of different ytterbium-doped gain media:

Some of these media are also used as ceramic gain media.

In most cases, the ytterbium dopant ions replace other ions (often yttrium) of the host medium, which have about the same size. For a good match of atomic size and weight, a high thermal conductivity can be maintained even at high doping levels.

High-power Operation

Very high efficiencies, diffraction-limited beam quality, and output powers of more than 1 kW have been achieved with ytterbium-doped double-clad fiber lasers and amplifiers. Thin disk lasers, which are most often working with Yb:YAG crystals, can also generate well above 1 kW diffraction-limited output with high beam quality, or even higher powers with non-diffraction-limited beam quality. Various Yb-doped gain media have been used in mode-locked lasers (see below) for the generation of femtosecond pulses; the by far highest average output powers of 80 W have been obtained with a thin disk Yb:YAG laser, passively mode-locked with a SESAM [10, 11].

Pulse Generation with Mode Locking

For passive mode locking, problems can arise in the form of Q-switching instabilities. This tendency is a consequence of the relatively small laser cross sections of ytterbium-doped media. Therefore, some of the broadband ytterbium-doped gain media are not very suitable for passively mode-locked lasers, particularly at high power levels, but can still be very useful in regenerative amplifiers. Relatively large cross sections are found for tungstate crystals.

Some ytterbium-doped crystals have a quite broad amplification bandwidth, but the emission curve is not very smooth; it exhibits several maxima. In such cases, wide wavelength tunability may still be achieved, but the realization of very short pulses with mode locking is difficult.

Quenching and Photodarkening

Due to the very simple level structure of the Yb3+ ion, it is widely believed that quenching effects are basically impossible. However, it has been discovered [7] that even strong quenching effects can occur in ytterbium-doped fibers. In that case, some fraction of the ytterbium ions – sometimes a few percent, sometimes more than 50% – then has an extremely shortened upper-state lifetime, whereas the other Yb ions are basically unaffected. The fraction of quenched ions strongly depends on the fabrication conditions. Even a small fraction is sufficient for strongly deteriorating the laser or amplifier performance, particularly for laser or pump wavelengths with strong absorption cross sections.

Another detrimental effect is photodarkening in Yb-doped fibers, a gradual degradation of fibers observed particularly in cases where a high ytterbium excitation density is required.

So far, only a quite limited amount of data on such effects is available, and the issues are not yet very well understood.

Ytterbium Codoping

Ytterbium doping is also often used together with erbium doping. Typically, the ytterbium ions absorb the pump radiation and transfer the excitation energy to the erbium ions. Even though the erbium ions could directly absorb radiation e.g. at 980 nm, ytterbium codoping can be useful because of the higher ytterbium absorption cross sections and the higher possible ytterbium doping density in typical laser glasses, so that a much shorter pump absorption length and a higher gain can be achieved. Ytterbium codoping is also sometimes used for praseodymium-doped upconversion fiber lasers.

Bibliography

[1]D. C. Hanna et al., "Continuous-wave oscillation of a monomode ytterbium-doped fiber laser", Electron. Lett. 24, 1111 (1988)
[2]P. Lacovara et al., "Room-temperature diode-pumped Yb:YAG laser", Opt. Lett. 16 (14), 1089 (1991)
[3]T. Y. Fan, "Heat generation in Nd:YAG and Yb:YAG", IEEE J. Quantum Electron. 29, 1457 (1993)
 [4]L. D. DeLoach et al., "Evaluation of absorption and emission properties of Yb3+ doped crystals for laser applications", IEEE J. Quantum Electron. 29 (4), 1179 (1993)
[5]A. S. Payne et al., "Ytterbium-doped apatite-structure crystals: A new class of laser materials", J. Appl. Phys. 75, 497 (1994)
[6]R. Paschotta et al., "Ytterbium-doped fiber amplifiers", IEEE J. Quantum Electron. 33 (7), 1049 (1997)
[7]R. Paschotta, et al., "Lifetime quenching in Yb doped fibers", Opt. Commun. 136, 375 (1997)
[8]C. Hönninger et al., "Ultrafast ytterbium-doped bulk lasers and laser amplifiers", Appl. Phys. B 69 (1), 3 (1999)
[9]F. Druon et al., "Apatite-structure crystal, Yb:SrY4(SiO4)3O, for the development of diode-pumped femtosecond lasers", Opt. Lett. 27 (21), 1914 (2002)
[10]E. Innerhofer et al., "60 W average power in 810-fs pulses from a thin-disk Yb:YAG laser", Opt. Lett. 28 (5), 367 (2003)
[11]F. Brunner et al., "Powerful RGB laser source pumped with a mode-locked thin-disk laser", Opt. Lett. 29 (16), 1921 (2004)
 [12]C. Kränkel et al., "Continuous wave laser operation of Yb3+:YVO4", Appl. Phys. B 79, 543 (2004)
[13]M. Rico et al., "Tunable laser operation of ytterbium in disordered single crystals of Yb:NaGd(WO4)2", Opt. Express 12 (22), 5362 (2004)
[14]J. Petit et al., "Laser emission with low quantum defect in Yb:CaGdAlO4", Opt. Lett. 31 (11), 1345 (2005)
 [15]Y. Zaouter et al., "47-fs diode-pumped Yb3+:CaGdAlO4 laser", Opt. Lett. 31 (1), 119 (2006)
 [16]C. Cascales et al., "Structural, spectroscopic, and tunable laser properties of Yb3+-doped NaGd(WO4)2", Phys. Rev. B 74, 174114 (2006)

See also: gain media, rare-earth-doped gain media, laser crystals, four-level and three-level gain media, neodymium-doped gain media, ceramic gain media, tungstate lasers, solid-state lasers, photodarkening, Spotlight article 2006-09-06

Categories: lasers, materials


Dr. R. Paschotta

This encyclopedia is authored by Dr. Rüdiger Paschotta, the founder and executive of RP Photonics Consulting GmbH. Contact this distinguished expert in laser technology, nonlinear optics and fiber optics, and find out how his technical consulting services (e.g. product designs, problem solving, independent evaluations, or staff training) could become very valuable for your business!

arrow
Home New articles Spotlight Feedback Advertising
Categories Search Quiz Links Pagehits
Y

This encyclopedia is provided by
RP Photonics Consulting GmbH.

Utilize the expertise of the author, Dr. Rüdiger Paschotta, also in the form of technical consulting services!

RP Q-switch

A powerful software tool for designing
Q-switched lasers. See the details.

TRUMPF logo

TRUMPF-Laser

a leading supplier of industrial diode pumped solid state lasers,
CO2 lasers, and laser systems for material processing.

Onefive logo

Onefive

Low-noise
femtosecond,
picosecond,
and tunable single-frequency lasers for OEM and R&D applications.

RP Fiber Power

This software helps to design and analyze fiber amplifiers and lasers.

Field Guide to Lasers

This new book by Dr. Paschotta explains principles and types of lasers.

A.L.S. logo

A.L.S. GmbH

Picosecond laser diodes
<30 ps, 375 - 1600 nm, >1 Wp, single shot - 120 MHz

Your Advertisement at This Place

will be seen by many thousands of visitors per month. These banners receive far over 100'000 page hits per month. Check the details.