High Quality Yb Research Articles

Investigation of Yb:CaWO4 as a potential new self-Raman laser crystal

High-quality Yb:CaWO4 crystal was grown using the Czochralski method; laser action and self-Raman conversion were demonstrated.

Investigation of the structure, optical properties and Cr4+ conversion level of Yb3+ and Cr3+ codoped YAG transparent ceramics

Abstract In this paper, the Cr4+ conversion level and optical characteristic of YAG transparent ceramics doped with various Cr3+ (0–0.25 at.%), Yb3+ (0-10 at.%) and Ca2+ (0-1.5 wt%) concentrations are investigated by morphology, XPS, EPR and spectral spectroscopy. It is determined that Yb ions doping will not only induce double R lines formation and asymmetry structure, but also decrease the conversion efficiency of tetrahedrally-coordinated Cr4+ ions in the Yb,Cr:YAG ceramics; these are both due to the emergence of Yb2+/Ca2+-F+ composite defect centers during vacuum sintering. The underlying mechanisms by which the cation doping influence the luminescence properties and affect the conversion efficiency of Cr4+ ion are discussed in detail using Huang-Rhys factor and theoretical calculation. It is also indicated that excessive CaO additives can improve microstructural homogeneity in Yb,Cr:YAG transparent ceramics; while barely increase the conversion efficiency of Cr4+ ions. A high-quality Yb,Cr:YAG transparent ceramic with CaO as a sintering aid is presented, with an optical transmittance of 84.5% at a wavelength of 1.2 μm, which is close to the single crystal transmittance value. This materials shows promise for passively self-Q-switched solid-state laser applications.

Efficient near-infrared laser emission and nonlinear optical properties of a newly developed Yb:LYSB laser crystal

Herein, we report on the growth and characterization of La0.78Y0.32Yb0.04Sc2.86(BO3)4 (Yb:LYSB) crystal as bifunctional laser and nonlinear optical (NLO) medium. High quality Yb:LYSB crystal with non-congruent melting has been grown by the Czochralski technique. Structural, linear and NLO properties, and near-infrared (NIR) laser emission performances of the grown crystal are presented. The absorption cross-section at 980 nm for σ-polarization was evaluated to be 0.6 × 10−20 cm2, and emission cross-section around 1080 nm in π-polarization and σ-polarization amounted to 3.6 × 10−21 cm2 and 1.33 × 10−21 cm2, respectively. The spectroscopic investigations revealed the existence of two different Yb3+ centers in the LYSB crystal matrix. Efficient laser emission at 1028 nm was obtained with a c-cut 4 at.% Yb:LYSB uncoated sample with a thickness of 3.5 mm. Employing the pump at 971.5 nm with a fiber-coupled diode laser, the Yb:LYSB medium yielded laser pulses with 1.5 mJ energy at 4.25 mJ energy of the absorbed pump pulse, corresponding to an overall optical-to-optical efficiency of 0.35. The laser operated with a high slope efficiency of 0.57. The refractive indexes were measured and the NLO properties of Yb:LYSB crystal for second harmonic generation of 1028 nm laser radiation were determined. The results of this work indicate Yb:LYSB as a promising crystal to design new laser sources in the NIR and green (∼514 nm) spectral ranges based on direct laser emission and self-frequency doubling processes, respectively.

The characteristics of high-quality Yb:YAG single crystal fibers grown by a LHPG method and the effects of their discoloration.

Single crystal fibers (SCFs), especially ytterbium (Yb) doped crystal fibers, have great potential in the field of high-power lasers. Colorless Yb:YAG single crystal fibers were fabricated using a laser heated pedestal growth (LHPG) method with a diameter fluctuation of less than 2% and a length to diameter ratio greater than 320 : 1. An abnormal color issue exists with respect to Yb:YAG crystals. The origin of coloration was studied via density functional theory, single-crystal X-ray diffraction, XPS and Raman spectroscopy and it was confirmed that the cyan coloration of Yb:YAG crystals is due to oxygen vacancies. Yb:YAG SCFs prepared via the LHPG method could avoid this type of defect due to the large specific surface area and melt convection caused by surface tension. The fundamental properties of the cyan Yb:YAG crystal source rod and colorless Yb:YAG SCFs were systematically investigated. The colorless Yb:YAG SCFs have higher infrared transmittance and thermal conductivity. The distributions of Yb3+ along the radial and axial directions were also measured. Meanwhile we demonstrated the propagation loss and a fiber laser using the colorless Yb:YAG SCFs, obtaining a minimum loss coefficient of 0.008 dB cm−1 and a maximum continuous-wave (CW) output power of 3.62 W. The colorless Yb:YAG SCFs with good thermal conductivity, low propagation loss, wide transparency and uniform ion distribution show promise for acting as the host material in single-mode lasers.

Growth and characterization of Yb:Ho:YAG single crystal fiber

High quality Yb and Ho co-doped Y3Al5O12 single crystal fibers have been successfully grown by the laser heated pedestal growth method of up to 124 mm in length and 450 μm in diameter for the first time. The results of inductively coupled plasma-atomic emission spectrometry analysis, X-ray diffraction and Raman spectroscopy reveal that the lattice structure and doping concentrations of the SCF are the same as that of the bulk. Scanning electron microscopy microphotographs shows that the fibers only have minor diameter fluctuations within 0.5%.

Effect of air annealing on the color center in Yb:Y3Al5O12 transparent ceramics with MgO as sintering additive

High quality Yb:Y3Al5O12 (YAG) transparent ceramics were fabricated by vacuum sintering with MgO as sintering aids. The Yb:YAG samples were annealed at 1250–1450°C for 20h in air. The experimental results showed that the transparency of Yb:YAG samples declined markedly with the annealing temperatures of 1250–1450°C. The samples became increasingly orange-yellow in color with the increase of annealing temperature. The potential reasons of discoloration were discussed for the first time. It was attributed to the complex color center [Mg2+F+] formed during the annealing, which was evidenced by optical absorption in the range of 300–500nm wavelength and the presence of an electron spin resonance (ESR) line at g=1.9806. The formation mechanism of the complex color center was explained in detail. The complex color center can be eliminated after post-HIP (hot isostatic pressing). And by air annealing and post-HIP, the transmittance of the samples increased from 80.3% to 83.4%.

Optical properties and laser performance of Yb-doped vanadates grown by floating zone method

We grew high-quality Yb:LuVO4, Yb:GdVO4, and Yb:YVO4 by the floating zone (FZ) method. It was found by measurement that these crystals had favorable optical properties. A maximum absorption coefficient of 27 cm−1 (FWHM) and a fluorescence bandwidth with a 20 nm (FWHM) were observed for Yb:LuVO4 at a Yb doping level of 4 at. %. Finally, we demonstrated the lasing performances of Yb:LuVO4, Yb:GdVO4, and Yb:YVO4. To our knowledge, this is the first time that a Yb-doped vanadate grown by the FZ method has been used as a laser, and 4 at.% Yb doping of the Yb:LuVO4 and Yb:YVO4 is the highest level of doping at which laser oscillation occurs among the Yb-doped vanadates.

Structural properties of host laser single crystal Yb:YAG

High quality Yb xY 1 − x AG (0 ≤ × ≤ 1) single crystals were grown by using the Czochralski method. The structural properties of Yb xY 1 − x AG (0 ≤ x ≤ 1) single crystals were also investigated using the EXAFS method. Additionally, for the first time, EXAFS results were compared with XRD results. Moreover, without essential lattice structure transformation, Yb xY 1 − x AG crystals can be found due to the varying of doping concentration in XRD measurements. However, EXAFS measurements indicated that the local fine structural variation around the Yb 3+ ion depends on the Yb 3+ concentration.

Diode-pumped efficient continuous-wave Yb:Y_3Ga_5O_12 laser at 1035 nm

An efficient diode-pumped Yb:Y3Ga5O12 (Yb:YGG) laser was demonstrated by using a high-quality Yb:YGG crystal grown by the optical floating zone method. Continuous-wave laser power up to 2.65 W had been obtained under an incident pump power of 6.71 W at 970 nm, corresponding to an optical-to-optical efficiency of 39.5% and maximum slope efficiency of 84.5%. A modeling calculation of the Yb:YGG laser was also performed, and the theoretical results were consistent with the experimental results.

Spectral properties of Yb:GdVO 4 crystals

Gadolinium vanadate (GdVO 4) is one of the most promising crystals and was introduced by Zagumennyi et al. [Sov. J. Quantum Electron. 22 (1992) 1071], which doped with rare-earth ions are attractive laser materials. Homogeneous high-quality Yb:GdVO 4 crystals were grown by the floating zone method. Absorption spectra and fluorescence spectra, as well as fluorescence decay curves of Yb:GdVO 4 crystals, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. The spectral properties and optical performance were investigated.

Bonding quality of Yb:Y3Al5O12/Y3Al5O12 composite crystals

The Yb:Y3Al5O12/Y3Al5O12 (Yb:YAG/YAG) composite crystals were prepared by thermal bonding method with different technological parameters. The bonding interface of the composite crystals were observed by optical microscope, scanning electron microscope, and atom force microscope. The light scattering experiments for bonding interface of the composite crystals were measured by the laser and transmission spectra. All experiments show that high-quality Yb:YAG/YAG composite crystals without space transition layer and light scattering on the bonding interface can be obtained by thermal bonding method under appropriate technological parameters.

Influence of the powder preparation on the sintering of Yb-doped Sc 2O 3 transparent ceramics

We report the preparation and the sintering of high quality Yb:Sc 2O 3 powders with the ultimate intent to make transparent Yb:Sc 2O 3 ceramics for laser applications. The aim of the study is to compare two routes of powder preparation and observe the influence of the powder processing on the sintering of Yb-doped Sc 2O 3 ceramics. The powders were prepared (i) either from commercial oxides by a classical ceramic way (solid state reaction process) (ii) or by a wet chemical route. In that case, a carbonate precursor was synthesized by a coprecipitation method from a mixed solution of scandium and ytterbium nitrates using aqueous ammonium hydrogen carbonate as a precipitating agent. The Yb:Sc 2O 3 powder was obtained after heat treatment of the carbonate precursor at 700 °C. The powders prepared by these two methods were characterized by BET measurements, XRD and SEM and their sintering behaviour was investigated by dilatometry. The effects of a grinding step and of the addition of a sintering aid addition (TEOS) were investigated. The microstructures of the vacuum sintered materials were observed by scanning electron microscopy. Electron probe microanalysis allowed to characterize the repartition of the dopant Yb 3+ in the Sc 2O 3 matrix. Translucent ceramics with densities close to 99% were obtained in the best conditions.

Growth and spectroscopic properties of Er,Yb : YCOB crystals

High quality Yb 3+ and Er 3+ co-doped YCa 4O(BO 3) 3 crystals were grown by the Czochralski method. Phase relationships between Y 3+/Yb 3+/Er 3+ and Ca 2+/B 3+ in the vicinity of the stoichiometric composition of YCa 4O(BO 3) 3 were discussed. The calculated absorption and emission cross sections were estimated. Efficient energy transfer from the excited Yb 3+ to the Er 3+ leads to strong emissions in the wavelength range of 1510–1580 nm peaking at 1535 nm. Lifetime of Er- 4I 11/2 was measured to be 1.23 ms. The energy transfer efficiency of 97% for Er 0.02Yb 0.2Y 0.78Ca 4O(BO 3) 3 crystal was estimated from the reduced lifetimes of the Yb 3+- 2F 5/2 level.

Floating zone growth and high-temperature hardness of YB 4 and YB 6 single crystals

High-quality YB 4 single crystals were prepared by controlling the composition of the atomic ratio, B/Y, of the molten zone to be 7–8. The preferential growth direction was almost normal to the (1 1 2) plane of the tetragonal crystal lattice, which had the lowest Vickers hardness. YB 6 crystals epitaxially grew on the YB 4 crystals. The growth rates of YB 4 and YB 6 crystals were inversely proportional to the difference in the composition between the crystal and the molten zone.