ytterbium-doped laser gain media (original) (raw)

Definition: laser gain media containing laser-active ytterbium ions

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Related: laser gain mediarare-earth-doped laser gain medialaser crystalsrare-earth-doped fibersquasi-three-level laser gain medianeodymium-doped laser gain mediaceramic laser gain mediatungstate laserssolid-state lasersphotodarkeningQuenching Degrades the Efficiency of Some Ytterbium-Doped Gain Media

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Contents

Introduction

Ytterbium (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 crystals, glasses and ceramics, also often in active optical fibers. It is often used in various types of high-power lasers and for wavelength-tunable solid-state lasers.

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

energy levels of ytterbium ions in Yb:YAG

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

Quasi-three-level Characteristics

The small quantum defect also has a usually unwanted consequence: the significant quasi-three-level behavior, particularly at short wavelengths. This 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 reflectance at the laser wavelength and a high transmittance 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, Ref. [6]).

Figure 2 shows the ytterbium transition cross-sections of a germanosilicate glass. Efficient pump absorption is possible around a wavelength of 910 nm 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 than for 910-nm pumping.

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. Yb3+:YAG), there is often a choice between different lasing transitions, where those with shorter wavelengths exhibit more pronounced three-level characteristics.

cross-sections of Yb:YAG

Figure 3: Absorption and emission cross-sections of Yb3+:YAG (data for 20 °C crystal temperature taken from Ref. [24]).

Figure 3 shows the ytterbium transition cross-sections of Yb3+:YAG. In this crystalline material, the absorption and emission peaks are less broad than in a glass. The dominant emission is around 1030 nm, but the weaker 1050-nm peak can also be utilized for laser operation.

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

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

In most cases, the ytterbium dopant ions replace other ions (often yttrium) of the host medium, which have a similar 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 most often work with Yb:YAG crystals, can also generate kilowatts of diffraction-limited output, or even higher powers with non-diffraction-limited beam quality.

Pulse Generation with Mode Locking

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 first 80 W at later even well over 200 W have been obtained with passively mode-locked thin-disk Yb:YAG lasers [13, 15, 26].

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 fairly 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 was 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 depends strongly on the fabrication conditions. Even a small fraction is sufficient for strongly reducing 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 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, ytterbium ions absorb the pump radiation and transfer the excitation energy to 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.

See the article on erbium-ytterbium-doped laser gain media for more details.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains 46 suppliers for ytterbium-doped laser gain media. Among them:

Exail

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Exail (formerly iXblue) offers a large choice of ytterbium-doped single clad and dual clad optical fibers to address a variety of laser performance requirements. Exail’s ytterbium-doped fibers have been designed to provide low noise and high optical conversion efficiency in fiber lasers and amplifiers at 1 ”m.

Our portfolio contains single clad, double clad, LMA and VLMA Yb fibers (from 5 ”m up to 40 ”m core diameter) in PM and non-PM versions. Space and radiation-resistant versions are also available.

Benefits and features:

Applications: 1-ÎŒm CW and pulsed lasers and preamplifiers.

Optogama

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Optogama offers a variety of ytterbium-doped crystals, including Yb:KGW, Yb:KYW, Yb:CaF₂, and others, known for their broad gain bandwidths, which enable the generation of femtosecond pulses in diode-laser pumped, mode-locked lasers.

Compared to other ytterbium-doped media, ytterbium-doped tungstates stand out due to their relatively high absorption and emission cross-sections, providing efficient laser performance.

Yb:CaF₂ is particularly valued for its very broad and smooth emission bands, superior thermal properties, and ability to be grown to large dimensions with excellent optical quality making it an ideal choice for high-power and ultrafast applications.

ALPHALAS

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Yb3+:YAG, Yb3+:CaF2 and other Yb3+-doped laser crystals are lately gaining more attention due to some unique lasing properties like very wide emission spectral range from 1020 nm to 1100 nm and the absence of excited-state absorption. Both the wide tuning range and generation of femtosecond laser pulses makes these laser gain media as the first choice for many applications.

Standard pre-configured Yb3+:YAG laser crystals with various doping levels from 0.5% to 10% and AR- or HR-coatings are available from stock. Customized designs are also available.

NKT Photonics

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Our ytterbium double clad fibers offer the largest single-mode cores in the world. They enable amplification to unprecedented power levels while keeping mode quality and stability. If you are building picosecond or femtosecond ultrafast fiber lasers, our Yb-doped aeroGAIN gain modules may be just what you are looking for.

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); doi:10.1364/OL.16.001089
[3] T. Y. Fan, “Heat generation in Nd:YAG and Yb:YAG”, IEEE J. Quantum Electron. 29 (6), 1457 (1993); doi:10.1109/3.234394
[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); doi:10.1109/3.214504
[5] A. S. Payne et al., “Ytterbium-doped apatite-structure crystals: a new class of laser materials”, J. Appl. Phys. 76 (1), 497 (1994); doi:10.1063/1.357101
[6] R. Paschotta et al., “Ytterbium-doped fiber amplifiers”, IEEE J. Quantum Electron. 33 (7), 1049 (1997); doi:10.1109/3.594865
[7] R. Paschotta, et al., “Lifetime quenching in Yb doped fibers”, Opt. Commun. 136, 375 (1997); doi:10.1016/S0030-4018(96)00720-1
[8] C. Hönninger et al., “Ultrafast ytterbium-doped bulk lasers and laser amplifiers”, Appl. Phys. B 69 (1), 3 (1999); doi:10.1007/s003400050762
[9] S. ChĂ©nais et al., “Multiwatt, tunable, diode-pumped CW Yb:GdCOB laser”, Appl. Phys. B 72, 389 (2001); doi:10.1007/s003400100477
[10] F. Druon et al., “Largely tunable diode-pumped sub-100-fs Yb:BOYS laser”, Appl. Phys. B 74, S201 (2002); doi:10.1007/s00340-002-0867-y
[11] 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); doi:10.1364/OL.27.001914
[12] P. Haumesser et al., “Determination of laser parameters of ytterbium-doped oxide crystalline materials”, J. Opt. Soc. Am. B 19 (10), 2365 (2002); doi:10.1364/JOSAB.19.002365
[13] 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); doi:10.1364/OL.28.000367
[14] J. Dong et al., “Dependence of the Yb3+ emission cross-section and lifetime on temperature and concentration in yttrium aluminum garnet”, J. Opt. Soc. Am. B 20 (9), 1975 (2003); doi:10.1364/JOSAB.20.001975
[15] F. Brunner et al., “Powerful RGB laser source pumped with a mode-locked thin-disk laser”, Opt. Lett. 29 (16), 1921 (2004); doi:10.1364/OL.29.001921
[16] C. KrĂ€nkel et al., “Continuous wave laser operation of Yb3+:YVO4”, Appl. Phys. B 79, 543 (2004); doi:10.1007/s00340-004-1635-y
[17] F. Druon et al., “Ultra-short-pulsed and highly-efficient diode-pumped Yb:SYS mode-locked oscillators”, Opt. Express 12 (20), 5005 (2004); doi:10.1364/OPEX.12.005005
[18] M. Rico et al., “Tunable laser operation of ytterbium in disordered single crystals of Yb:NaGd(WO4)2”, Opt. Express 12 (22), 5362 (2004); doi:10.1364/OPEX.12.005362
[19] J. Petit et al., “Laser emission with low quantum defect in Yb:CaGdAlO4”, Opt. Lett. 30 (11), 1345 (2005); doi:10.1364/OL.30.001345
[20] Y. Zaouter et al., “47-fs diode-pumped Yb3+:CaGdAlO4 laser”, Opt. Lett. 31 (1), 119 (2006); doi:10.1364/OL.31.000119
[21] M. Laroche et al., “Accurate efficiency evaluation of energy-transfer processes in phosphosilicate Er3+-Yb3+-codoped fibers”, J. Opt. Soc. Am. B 23 (2), 195 (2006); doi:10.1364/JOSAB.23.000195
[22] C. Cascales et al., “Structural, spectroscopic, and tunable laser properties of Yb3+-doped NaGd(WO4)2”, Phys. Rev. B 74 (17), 174114 (2006); doi:10.1103/PhysRevB.74.174114
[23] D. Li et al., “Characterization of laser crystal Yb: CaYAlO4”, J. Opt. Soc. Am. B 28 (7), 1650 (2011); doi:10.1364/JOSAB.28.001650
[24] J. Koerner et al., “Measurement of temperature-dependent absorption and emission spectra of Yb:YAG, Yb:LuAG, and Yb:CaF2 between 20 °C and 200 °C and predictions on their influence on laser performance”, J. Opt. Soc. Am. B 29 (9), 2493 (2012); doi:10.1364/JOSAB.29.002493
[25] M. Vivona et al., “Influence of Ce3+ codoping on the photoluminescence excitation channels of phosphosilicate Yb/Er-doped glasses”, IEEE Photon. Technol. Lett. 24 (6), 509 (2012)
[26] C. J. Saraceno et al., “Ultrafast thin-disk laser with 80 ÎŒJ pulse energy and 242 W of average power”, Opt. Lett. 39 (1), 9 (2014); doi:10.1364/OL.39.000009

(Suggest additional literature!)

Picture of Dr. RĂŒdiger Paschotta

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