Search

Yb:CaF2 transparent ceramics represent a promising laser gain medium for ultra-short lasers due to their characteristics: low phonon energy, relatively high thermal conductivity, negative thermo-optical coefficient, and low refractive index. Compared to single crystals, Yb:CaF2 ceramics offer superior mechanical properties, lower cost, and it is easier to obtain large-sized samples with proper shape and uniform Yb3+ doping at high concentrations. The combination of air pre-sintering and Hot Isostatic Pressing (HIP) emerges as a viable strategy for achieving high optical quality and fine-grained structure of ceramics at lower sintering temperatures. The properties of the powders used in ceramic fabrication critically influence both optical quality and laser performance of Yb:CaF2 ceramics. In this study, the 5 atomic percentage (at.%) Yb:CaF2 transparent ceramics were fabricated by air pre-sintering and hot isostatic pressing (HIP) using nano-powders synthesized through the co-precipitation method. The co-precipitated powders were optimized by studying air calcination temperature (from 350 to 550 °C). The influence of calcination temperature on the microstructure and laser performance of Yb:CaF2 ceramics was studied in detail. The 5 at.% Yb:CaF2 transparent ceramics air pre-sintered at 625 °C from powders air calcined at 400 °C and HIP post-treated at 600 °C exhibited the highest in-line transmittance of 91.5% at 1200 nm (3.0 mm thickness) and the best laser performance. Specifically, a maximum output power of 0.47 W with a maximum slope efficiency of 9.2% at 1029 nm under quasi-CW (QCW) pumping was measured. [ABSTRACT FROM AUTHOR]

Highly transparent 10 at.% Yb:GdxY3−xAl5O12 (x = 0.3, 0.5, and 0.7) ceramics were successfully fabricated by vacuum solid‐state reactive sintering at 1800°C for 20 h combined with hot isostatic pressing posttreatment at 1700°C for 3 h under 176 MPa pressure in Ar atmosphere. The in‐line transmittances of these ceramics with the thickness of 2.5 mm are 84.4%, 84.0%, and 83.5% at 1100 nm for x = 0.3, 0.5, and 0.7, respectively. The relationships of the Gd3+ content among the phase, microstructures, spectral, and laser properties of the Yb:GdxY3−xAl5O12 ceramics were elucidated in detail. The introduction of Gd3+ has a little influence on the crystal field strength of the Yb3+ sites in GdxY3−xAl5O12. The absorption, emission spectra, and fluorescence lifetime of the Yb3+ in these ceramics are similar, close to 10 at.% Yb:YAG ceramics. Quasi‐continuous wave laser outputs of the ceramics were also achieved. The maximum laser output powers are 7.8, 7.7, and 6.6 W with the corresponding slope efficiency as 46.2%, 44.7%, and 39.2% for x = 0.3, 0.5, and 0.7, respectively. The 7.8 W laser output power is the highest value achieved so far for the Yb:GdYAG ceramics, to the best of our knowledge. The previous discussions show that not all the mixed garnets could enhance full width at half maximum of absorption and emission peaks for the active ions; however, the Yb:GdYAG ceramics are still excellent laser gain media. [ABSTRACT FROM AUTHOR]

In this work, 5at.% Yb:Lu2O3 transparent ceramics were air‐annealed at different temperatures to eliminate oxygen vacancies for laser performance improvement. The influence of annealing temperature on microstructures, optical quality, and laser performance was investigated comprehensively. The ceramics HIP (Hot isostatic pressing) post‐treated at 1750°C and annealed above 1100°C show a significant optical quality decrease due to residual pore expansion, and the ceramic sample annealed at 900°C shows better laser performance than others. The maximum output of 2.88 W was obtained at 1033.3 nm with a slope efficiency of 37.4% under a quasi‐continuous wave (QCW) mode. Note that 5at.% Yb:Lu2O3 transparent ceramics HIP post‐treated at 1550°C still keep good transparency even when being annealed at 1300°C due to less residual compressed pores. The highest slope efficiency is about 73.8% with a maximum output power of 2.84 W under QCW. Fine‐grained and dense Yb:Lu2O3 transparent ceramics could be annealed at higher temperatures to eliminate oxygen vacancies more thoroughly to improve laser performance. [ABSTRACT FROM AUTHOR]

5at.% Yb:Lu2O3 transparent ceramics were fabricated successfully by vacuum sintering along with hot isostatic pressing posttreatment from the nanopowders. The influences of calcination temperature on morphology and microstructures of powders and ceramics were studied systematically. The optimal ceramic sample from the nanopowder calcined at 1050°C shows uniform and dense microstructure with the in‐line transmittance of 81.5% at 1100 nm. The results of the thermal measurements, that is, thermal conductivity and specific heat, were related to the changes occurring in the microstructure of the ceramics studied. It was shown on this basis that appropriate control of the technological process of sintering ceramics makes it possible to obtain laser ceramics with very good thermal properties as well as maintaining their high optical quality. Concerning the laser performance, the highest‐optical quality 5at.% Yb:Lu2O3 sample was pumped in quasi‐continuous wave conditions measuring a maximum output power of 2.59 W with a corresponding slope efficiency of 32.4%. [ABSTRACT FROM AUTHOR]

Transparent 4 at.% Tm:Y3ScAl4O12 (Tm:YSAG) laser ceramics were fabricated by solid‐state reaction combined with vacuum sintering method. The 4 at.% Tm:YSAG ceramic sample sintered at 1800°C for 30 hours possesses homogenous microstructure and excellent optical properties, showing a transmittance of 79.3% at 2000 nm. The absorption and emission spectra of the Tm:YSAG ceramics are studied and compared with those of 4 at.% Tm:Y3Al5O12 ceramics. The introduction of Sc3+ greatly affects the energy levels of the Tm3+, causing the disappearance and degeneration of some absorption and emission peaks in the middle infrared region. The laser performance of the 4 at.% Tm:YSAG ceramics is also tested in the Quasi‐continuous‐wave (QCW) mode by pumping with a 790 nm laser diode (LD). A maximum laser output power of 0.54 W with a slope efficiency of 4.8% is achieved, which is the first laser output for Tm:YSAG ceramics. [ABSTRACT FROM AUTHOR]

Transparent Yb:Y3ScAl4O12 (Yb:YSAG) ceramics with different ytterbium doping concentrations such as 5, 10, 15, 20 at.% have been successfully fabricated by solid‐state reactive sintering. All the obtained ceramics are in dense and homogeneous structure after sintering at 1820°C for 30 hours and with a posttreatment by hot isostatic pressing at 1750°C for 3 hours with 200 MPa pressure. We systematically analyzed the influence of Yb3+ doping concentration on the microstructure and optical properties of the ceramics. The 10 at.% Yb:Y3ScAl4O12 ceramics with a thickness of 3.2 mm show the best transparency as high as 80.9% at 1100 nm. The laser emission of the 10 at.% Yb:YSAG ceramics was tested, resulting in a maximum slope efficiency of 67.6% and a maximum output power of 11.3 W under quasi‐continuous wave pump conditions. The tuning range spanned from 990 to 1071 nm. [ABSTRACT FROM AUTHOR]

In this article, 5 at.% Yb:Lu2O3 transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) posttreatment using co‐precipitated nano‐powders. The influence of precipitant molar ratio, ammonium hydrogen carbonate, to metal ions (AHC/M3+, R value) on the properties of Yb:Lu2O3 precursors and calcined powders was investigated systematically. It was found that the powders with different R value calcined at 1100°C for 4 hours were pure cubic Lu2O3 but the morphologies of precursors and powders behaved differently. The opaque samples pre‐sintered at 1500°C for 2 hours grew into transparent ceramics after HIP posttreatment at 1750°C for 1 hour. The final ceramic with R = 4.8 showed the best optical quality with the in‐line transmittance of 79.7% at 1100 nm. The quasi‐CW laser operation was performed at 1034 nm and 1080 nm with a maximum output power up to 8.15 W as well as a corresponding slope efficiency of 58.4%. [ABSTRACT FROM AUTHOR]

• Impact of different vacuum sintering temperatures and HIP processes on microstructure, optical and lasing properties of Yb:Sc 2 O 3 ceramics. • Evaluation of the effects of vacuum sintering temperature on 3at.% Yb:Sc 2 O 3 ceramics grain size. • High optical quality samples with high laser efficiency obtained directly from commercial powders, without any laboratory synthesis phase. In this paper we report on the preparation and laser performance of transparent 3 at. % Yb:Sc 2 O 3 ceramics by reactive sintering of commercially available powders under vacuum followed by hot isostatic pressing (HIP). Combinations of different vacuum sintering temperatures (1650 °C and 1750 °C) and different HIP treatments (1700 °C and 1800 °C at 200 MPa) were tested in order to understand how these steps influence the microstructure and thus the optical and lasing properties of the ceramic samples. All the samples showed a good optical quality. The microstructure analysis and the laser tests showed that the vacuum pre-sintering temperature is the key factor determining the quality of the samples and the laser performances. The best values of slope efficiency i.e. η L = 50 % and output power i.e. P out = 6.62 W were obtained for the sample pre-sintered under vacuum at 1650 °C and hot isostatically pressed at 1800 °C. [ABSTRACT FROM AUTHOR]

The 5 at.% Yb:CaF 2 transparent ceramics were successfully fabricated by hot pressing (HP) combined with hot isostatic pressing (HIP) for the first time. The raw nano-powders were synthesized by the co-precipitation method and the influence of HP temperature and HIP post-treatment on the optical quality and microstructures of Yb:CaF 2 transparent ceramics were investigated. After HIP post-treatment (600 °C × 3 h, 100 MPa Ar), the micro pores in the hot pressed ceramics were further eliminated and all ceramics revealed high optical quality. The ceramic sample hot pressed at 575 °C for 2 h and HIP post-treated at 600 °C for 3 h shows the best optical quality with the in-line transmittance of 90.5% at 1200 nm (3.9 mm thickness), and the average grain size of ceramics is only 470 nm. And the absorption and emission cross sections of ceramics were calculated. Finally, the laser performance of 5 at.%Yb:CaF 2 transparent ceramics was tested. The maximum output power of ceramics was 1.12 W, which is higher than other Yb:CaF 2 ceramics fabricated by pressure-assisted sintering method reported in literature, with a corresponding, slope efficiency of 11.6%. • Yb:CaF 2 transparent ceramics were prepared by hot pressing and HIP post-treatment. • Yb:CaF 2 transparent ceramics showed high in-line transmittance of 90.5% at 1200 nm. • A maximum output power of 1.12 W was achieved for Yb:CaF 2 transparent ceramics. [ABSTRACT FROM AUTHOR]

Transparent ytterbium doped calcium-fluoride (Yb:CaF 2) ceramics were successfully fabricated by air pre-sintering and hot isostatic pressing (HIP) post-treatment from the powders synthesized by the co-precipitation method. The influence of pre-sintering temperature on the densification, microstructures and optical quality of 5 at.% Yb:CaF 2 ceramics was systematically investigated. The ceramic sample pre-sintered at 650 °C for 2 h and HIP post-treated at 650 °C for 1 h shows the best transparency with the in-line transmittance of 90% at 1200 nm. The upper level lifetime of the Yb3+ in Yb:CaF 2 ceramics was evaluated to be 1.95 ms by the pinhole method. In addition, the laser emission from an optimized 5 at.% Yb:CaF 2 ceramic sample yields in the maximum output power of 0.81 W with a maximum slope efficiency of 22.6% at 1028.5 nm under quasi-CW pumping. • Yb:CaF 2 nano-powders were synthesized by the co-precipitation method. • Yb:CaF 2 ceramics with the in-line transmittance of 90% were obtained by air pre-sintering and HIP post-treatment. • Yb:CaF 2 ceramic laser with the slope efficiency of 22.6% and the output power of 0.81 W was obtained at 1028.5 nm. [ABSTRACT FROM AUTHOR]

Abstract: Transparent 9.8at% Yb:YAG ceramic samples were prepared by reactive sintering of commercial oxides and using 0 or 1wt% polyethylene glycol (PEG) as dispersant. The optical quality of the samples turns out to be improved by using a dispersant and optical transmittance close to the commercial samples has been obtained. On the other hand the laser characterization evidenced the activation of a non-linear loss mechanism occurring only in the sample containing PEG and despite its better optical quality, at high excitation level. A SEM analysis of material microstructure could not explain this behavior. A state of the art TEM analysis at nanometric scale was performed providing high resolution chemical spectroscopic results that indicate the presence of amorphous and crystalline silicate phases playing different roles in the two samples. [Copyright &y& Elsevier]

Abstract: This article focuses on the importance of the ceramic production process for the final transparency and overall optical quality of materials to be used as laser hosts. YAG-based ceramics are prepared starting from commercial powders. The materials are prepared by reactive sintering in a clean atmosphere and under high vacuum. Nd or Yb are selected as active elements as the more appropriate for high energy and high peak power lasers. The powder type and treatment and the solvent removal technique are described in detail as well as the experimental conditions adopted during shaping. The influence of the pre-sintering and sintering cycles on the reaction among the involved oxides and on the microstructure after sintering is shown. The optical characterization is also reported. [Copyright &y& Elsevier]

• First systematic microstructural and spectroscopic study of Yb: (Lu x ,Y (1−x)) 2 O 3 sesquioxide laser ceramics • Application of the laser ablation of the production of well –mixed nanoparticles as starting material for the ceramics. • Characterization of the microstructural properties (lattice constant, grain size, etc.) for different Lu/Y ratio. • Characterization of the internal crystalline phase homogeneity at sub-μm level by means of micro-Raman spectroscopy. • Characterization of the spectroscopic properties of Yb3+ as lasing dopant (absorption, emission, upper laser level lifetime). We report an in-depth investigation (fabrication, microstructure and spectroscopy) of Yb3+-doped mixed sesquioxide transparent ceramics (Lu x Y 1−x) 2 O 3 with x = 0, 0.113 and 0.232. The ceramics were fabricated by vacuum sintering of nano-sized particles synthesized by CO 2 laser co-evaporation of the corresponding solid targets with different Y/Lu balance. The effect of Lu3+ concentration on crystal structure and phase evolution of the nanopowders and microstructure, optical and spectroscopic properties of the sintered ceramics was investigated. The micro-Raman measurements with high spatial resolution revealed a homogeneous distribution of both yttrium and lutetium in the mixed composition. The optical transmission of 1.4 mm-thick ceramics was over 80% in the wavelength range of 500–1100 nm. Partial substitution of Y3+ cations for Lu3+ cations determines a small shift toward longer wavelengths and broadening of the Yb3+ main emission peaks at about 1030 and 1076 nm. This is the first extensive characterization of the spectroscopic properties of Yb:(Y,Lu) 2 O 3 compositional family in ceramic hosts. [ABSTRACT FROM AUTHOR]

We studied the laser performances of a new family of Yb3+-doped mixed sesquioxide ceramics, (Lu x Y 1-x) 2 O 3 with x = 0.113 and 0.232, fabricated by vacuum sintering of nano-sized particles synthesized by CO 2 laser co-evaporation of solid targets with different Y/Lu balance. Their microstructural and spectroscopic properties were reported in details in a companion paper. We report the results of the laser emission performances (slope efficiency, output power and tuning range) under semiconductor laser pumping. A comparison of the performance with a 5.6 at% Yb:Y 2 O 3 ceramics fabricated with the same method is reported. A maximum slope efficiency of 68.1% was obtained in quasi -CW emission regime from the sample with x = 0.113, with a wavelength tunability range from 994 to 1089 nm full width (i.e. 95 nm). Moreover, from the sample with Yb:Y 2 O 3 composition we obtained a maximum slope efficiency of 74% (optical conversion efficiency 68.3%), among the highest ever reported for ceramic Yb:Y 2 O 3. This is the first extensive characterization of the laser performances of the Yb:(Y,Lu) 2 O 3 composition in ceramic hosts. • First extensive study of the laser emission of Yb3+:(Lu x Y 1-x) 2 O 3 ceramics with various Lu/Y ratio(x = 0; 0.113 and 0.232). • Highly efficient laser Yb:(Lu,Y) 2 O 3 mixed sesquioxide ceramic sample fabricated by vacuum sintering of nanoparticles. • Maximum slope efficiency of 68.1% in quasi-CW regime from the sample with x = 0.113; wavelength tuning 994-1089 nm full width. • Comparison of the performance with a 5.6 at.% Yb:Y 2 O 3 ceramics fabricated with the same method. [ABSTRACT FROM AUTHOR]

In this paper, we reported mixed garnet laser ceramic gain media with composition of 15 at.% Yb:Lu x Y 3-x Al 5 O 12 (x = 0, 0.75, 1.5, 3.0, Yb:LuYAG) fabricated by the solid state reactive sintering in vacuum. After being sintered at 1850 °C for 30 h, all the Yb:LuYAG ceramics have dense microstructure and high optical quality. The in-line transmittances of the 1.6 mm thick ceramics with x = 0, 0.75, 1.5 and 3.0 are 84.8%, 84.1%, 82.4% and 83.4% at 1100 nm wavelength, respectively. The influences of the Lu3+ content on the absorption and emission spectra were discussed. With the increase of Lu3+ content, the crystal field increases, causing a blue shift of position and bigger absorption coefficient of the about 938 nm absorption peaks. The main emission peaks for all Yb:LuYAG ceramics retain at 1030 nm. The samples have shown a high laser emission slope efficiency, near to exceeding 60% in optimized output coupling conditions. The comparable optical properties and excellent thermo-mechanical qualities mean that the Yb:LuYAG ceramics are promising gain media used for high power laser application. • Yb:LuYAG ceramics with the in-line transmittance over 82% at 1100 nm were fabricated by reactive sintering. • The introduction of Lu3+ caused the blue shift and bigger absorption for Yb:Lu x Y 3-x Al 5 O 12 ceramics at ~938 nm. • For Yb:Lu x Y 3-x Al 5 O 12 ceramics with x = 0.75, the laser outpower of 8.7 W and the slope efficacy of 65.6% were obtained. [ABSTRACT FROM AUTHOR]

10 at.% Yb:Y 3 Sc x Al 5-x O 12 (x = 0.25, 0.5, 1.0 and 1.5) transparent ceramics have been successfully fabricated by the solid state reaction method combined with vacuum sintering, whose transmittances reach 80% at 1100 nm with thickness of 3.0 mm. The full width at half maximum (FWHM) of the emission peaks located at about 1030 nm increases for increasing the Sc3+ content, and a maximum FWHM of 14.53 nm is obtained for 10 at.% Yb:Y 3 Sc 1.5 Al 3.5 O 12 ceramics, which is 1.4 times larger than that of the 10 at.% Yb:Y 3 Al 5 O 12 (Yb:YAG) ceramics. Finally, the laser performance of the 10 at.% Yb:Y 3 Sc 1.5 Al 3.5 O 12 ceramics was tested and compared with that of a standard 10 at.% Yb:YAG sample. In quasi continuous wave (QCW) regime, a maximum laser output power of 10.8 W was obtained with the slope efficiency of 66.4%. The tuning range significantly broadens in the case of the Yb:YSAG sample, reaching a width of 86.2 nm. • 10 at.% Yb:Y 3 Sc x Al 5-x O 12 transparent ceramics were fabricated by solid state reactive sintering. • FWHM of the emission peaks of Yb:Y 3 Sc x Al 5-x O 12 ceramics increases with increasing the Sc content. • A maximum QCW laser output power of 10.8 W was obtained in the 10 at.% Yb:Y 3 Sc 1.5 Al 3.5 O 12 ceramics. [ABSTRACT FROM AUTHOR]