Search

A high-power monolithic continuous wave (CW) Yb doped fiber amplifier at 1064 nm has been demonstrated based on traditional large mode area step-index fiber, which generated 5.07 kW narrow line-width laser with near diffraction-limited beam quality. At the maximal output power, >35dB OSNR has been achieved with line-width being 370pm, and the measured beam quality is M2x = 1.252, M2y = 1.322. The influence of cooling temperature on SRS has been investigated in high power fiber lasers, which shows that the SRS at 4kW has been suppressed 24 dB by lowering the temperature from 20°C to 8°C. To the best of our knowledge, this is the highest narrow line-width laser power generated from the traditional large mode area step-index monolithic fiber amplifier.

104 W supercontinuum (SC) covering 370 nm-2400 nm is reported. High power visible SC is generated by pumping cascaded photonic crystal fibers (PCF) with 1064 nm picosecond pulse. Cascaded PCFs is fabricated by fusion splicing two different PCFs together with a coupling efficiency of 75%. For the purpose of avoiding fiber fuse phenomenon in PCF, the discharge time and intensity of fusion splicer should be precisely controlled. Two components of cascaded PCFs are pumped separately by 1064 nm picosecond pulse for comparing with the impact of cascaded PCFs. As a result of pumping cascaded PCFs, 104 W SC covering 370 nm-2400 nm is generated. Visible spectra (380 nm-780 nm) accounts for 50.4% (52.4 W) by numerical integration. To best of our knowledge, it's the first time that a visible SC with over a hundred watt output and 370 nm short-wave edge is obtained experimentally.

Transition metal dichalcogenides (TMD) are regarded as suitable substitutes for precious Pt as the hydrogen evolution catalysts due to their low cost and unique electronic structure. However, the bulk crystals of these materials are good conductors but show poor catalytic performance, whereas their nanostructures exhibit better activity but lower conductivity. In this study, a self-supported three-dimensional (3D) porous nitrogen-doped nickel selenide (N NiSe2) electrode is constructed and its HER activities over a wide range of pH are evaluated. Especially, only an overpotential of 86 mV is needed to afford the current density of 10 mA cm−2 in an alkaline medium (1.0 M KOH, pH = 14). Density functional theory (DFT) calculations show that N NiSe2 has lower Gibbs free-energy of H (ΔGH*) and water adsorption energy (ΔGH2O*) compared to pristine NiSe2, revealing that the catalyst-H* and catalyst-H2O state are easily to occur on the surface of N NiSe2 and finally enhance the HER activity. The as obtained N NiSe2 can be a potential non-noble-metal catalyst for practical hydrogen evolution reaction application.

We fully demonstrated an ytterbium (Yb) doped triple-clad laser fiber with intense pump absorption, high efficiency, and laser stability. P5+/Al3+ molar ratio in the central region of fiber core was specially designed to be ~1.08 for compensating P2O5 evaporation, while the ratio in the outer region was set as ~0.92 for obtaining a flattened refractive index profile. Applying a two-stage deposition process, one-time collapse technique, low-temperature multi-times sintering, and suitable flow of pure POCl3 during sintering and collapsing process were instrumental in decreasing and offsetting element evaporation. Measured in an all-fiber master oscillator power amplifier configuration, the 7-m-long fiber obtained 1.39 kW near-single-mode laser output at 1079.6 nm with a slope efficiency of 85.2% and a beam quality M2 of 1.36. Output laser spectrum with no sign of nonlinear-related peaks and a narrow 3-dB-bandwidth of ~0.33 nm was obtained. The fiber-based laser setup was kept at the maximum power for 1 h with power degradation less than 0.21%. The results demonstrated Yb-doped aluminophosphosilicate triple-clad fiber is a highly competitive candidate for commercial high-power laser and high-power narrow-linewidth fiber laser.

To ensure sufficient absorption of tandem-pumping energy, a large-scale aluminophosphosilicate fiber with 55 μm core and 400 μm inner-clad in diameter, i.e., a 55/400 Yb-APS fiber, was experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Based on an all-fiberized master oscillator power-amplifier laser setup tandem-pumped by 1018 nm fibber laser, a 150 W 1080 nm seed was amplified to 11.18 kW successfully, along with an optical-to-optical efficiency of 79.7%.

The average power scaling of counter pumped Yb-doped monolithic fiber amplifiers emitting a diffraction-limited beam has been investigated. The characteristics of seed laser including linewidth and power are optimized, which are beneficial for the suppression of stimulated Brillouin scattering (SBS), nonlinear-induced spectral broadening and transverse mode instabilities (TMI). The fiber with a mode field area of 700 μm2 is able to amplify a 360 W narrow linewidth seed up to 4.05 kW average output power before the onset of TMI. Up to this power level, a narrow linewidth with (0.372 nm), high optical-to-optical efficiency of 67.6% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -52 dB is obtained.

A 1178 J near diffraction limited 527 nm laser is realized in a complete closed-loop adaptive optics (AO) controlled off-axis multi-pass amplification laser system. Generated from a fiber laser and amplified by the pre-amplifier and the main amplifier, a 1053 nm laser beam with the energy of 1900 J is obtained and converted into a 527 nm laser beam by a KDP crystal with 62% conversion efficiency, 1178 J and beam quality of 7.93 times the diffraction limit (DL). By using a complete closed-loop AO configuration, the static and dynamic wavefront distortions of the laser system are measured and compensated. After correction, the diameter of the circle enclosing 80% energy is improved remarkably from 7.93DL to 1.29DL. The focal spot is highly concentrated and the 1178 J, 527 nm near diffraction limited laser is achieved.

A 20μm-to-50μm monolithic MFA has been designed and fabricated by only one-step-tapering. With the MFA, 1kW laser beam with nearly diffraction-limited beam quality has been demonstrated after 15m propagation in highly multimode 50μm/0.11 NA fiber with different bend diameters.

We present a theoretical study of mode evolution in high-power distributed side-coupled cladding-pumped (DSCCP) fiber amplifiers. A semi-analytical model taking the side-pumping schemes, transverse mode competition, and stimulated thermal Rayleigh scattering into consideration has been built, which can model the static and dynamic mode evolution in high-power DSCCP fiber amplifiers. The mode evolution behavior has been investigated with variation of the fiber amplifier parameters, such as the pump power distribution, the length of the DSCCP fiber, the averaged coupling coefficient, the number of the pump cores and the arrangement of the pump cores. Interestingly, it revealed that static mode evolution induced by transverse mode competition is different from the dynamic evolution induced by stimulated thermal Rayleigh scattering. This shows that the high-order mode experiences a slightly higher gain in DSCCP fiber amplifiers, but the mode instability thresholds for DSCCP fiber amplifiers are higher than those for their end-coupled counterparts. By increasing the pump core number and reducing the averaged coupling coefficient, the mode instability threshold can be increased, which indicates that DSCCP fibers can provide additional mitigation strategies of dynamic mode instability.

A backward (6+1)×1 pump and signal combiner has been presented, which can combine >5kW pump power in brightness-loss operation mode. By optimizing the fabrication technology, the beam quality (M2) degradation has been controlled to be less than 0.1.

In this Letter, the amplified spontaneous emission (ASE) effect of a 1030 nm fiber laser is studied theoretically and, based on the theoretical results, a 3 kW high optical signal-to-noise ratio (OSNR) 1030 nm fiber amplifier with a 180 pm linewidth and near-diffraction-limited beam quality is achieved. A theoretical model, which takes simulate ASE light falling in the range of Raman light as the Raman seed, has been used to optimize the power scaling capability of 1030 nm fiber amplifiers. It shows that the SRS effect seeded by the ASE is the main limiting factor for the fiber amplifiers operating at 1030 nm, and > 3 k W output power with a high OSNR can be achieved by proper parameter designing of the fiber laser system. A 1030 nm monolithic narrow linewidth fiber amplifier, which delivers 3 kW output power with the OSNR being 37 dB and a 0.18 nm spectrum linewidth, has been demonstrated. At the maximum 3 kW output power, the SRS light peak is obviously higher than ASE light, which agrees with the theoretical predictions. Neither a stimulated Brillouin scattering effect nor a thermal-induced mode instability effect has been observed at ultimate power level, and the beam quality factor M 2 is measured to be less than 1.2. To the best of our knowledge, this is the highest average power for a narrow linewidth single-channel fiber laser system reported so far operating at 1030 nm.

To investigate the laser performance and material characters of Ce/Yb/F-codoped aluminosilicate binary glass fiber, we took commercial Nufern-20/400–9 M fiber as a research object. 1.83 kW laser output power at 1066 nm with an optical-to-optical efficiency of 81.7% was achieved in master oscillator power amplifier (MOPA) system. No power roll-over was found for about 1 h at the maximum power, indicating Nufern-20/400-9M fiber has excellent power stability. Ce3+ ions can effectively suppress the regular photodarkening phenomenon easily-observed in Yb-doped aluminosilicate glass fiber. However, as the laser output power exceeded 1 kW, optical nonlinearities, such as four-wave-mixing and stimulated Raman scattering, emerged and the beam quality factor M2 degraded heavily from 1.60 for 1 kW to 2.37 for 1.8 kW. The studying results show that Nufern-20/400-9M fiber with strong nonlinearities and low threshold of modal degradation in the MOPA system which is suitable for kW-level fiber laser applications.

In this paper, the model to simulate the impact of bend induced mode distortion on the beam quality and mode instability (MI) threshold of fiber amplifier is established, and the results show that the bend induced mode distortion will degrade the beam quality of fiber laser and decrease the MI threshold. The bend induced mode distortion will change the gain of active fiber, then destroy the beam quality of fiber amplifier, and decrease the MI threshold, but the bend loss will suppress high order mode. Therefore, with the decreasing of fiber bend radius, the MI threshold will decrease firstly, and then increase.

We fabricated an Yb-doped triple-clad fiber consisting in adding to aluminophosphosilicate core and F300-pump cladding, low-refractive-index fluorine doped silica cladding, and demonstrated its laser performance based on an all-fiber oscillator. MCVD system, all-gas-phase chelate precursor doping technique, and a simple overcladding process were applied to make Yb-doped aluminophosphosilicate triple-clad fiber preform. Ultra-thin substrate tube and a two-stage deposition process were proposed to decrease and offset elements evaporation. The outer region of fiber core was tested with ∼1050 ppm Yb2O3, ∼10,800 ppm Al2O3, and ∼9950 ppm P2O5, while the central region was doped with ∼600 ppm Yb2O3, 8100 ppm Al2O3, and ∼7000 ppm P2O5, respectively (ppm is in molar here). Two-stage deposition process and triple-clad design results in pump absorption from Yb3+ ions about 0.67 dB/m at 915 nm. Tested in an all-fiber oscillator configuration forward-pumped by 915 nm laser diodes, 28 m-long triple-clad fiber presented 560 W laser output with optical-to-optical efficiency of 68.7%, and the corresponding beam quality M2 is ∼1.18. The results indicate all-gas-phase chelate precursor doping technique in combination with overcladding technique is potential to manufacture high power triple-clad fiber, and ultra-thin substrate tube as well as two-stage deposition process are very effective ways to decrease and offset element evaporation.

By using the MCVD system and the all-gas-phase chelate precursor doping technique, we fabricated an Yb-doped aluminophosphosilicate fiber with 20 μm-core and 400 μm-clad in diameter, i.e., 20/400 Yb-APS fiber. The fiber core was doped with 1100 ppm Yb3+, 7200 ppm Al3+, and 8000 ppm P5+. With a molar ratio of Al/P close to 1:1, low refractive index difference and suitable numerical aperture was obtained for large-mode-area fiber design. Directly forward pumped by 976 nm laser diodes, 11-m-long 20/400 Yb-APS fiber presented 3.03 kW laser output at 1080 nm with a slope efficiency of 76.6% and beam quality M2 of ∼1.58. Up to this power level, no signs of instable beam profile, beam quality worsening, and laser power roll-over were obtained, indirectly justified no obvious mode instability in the whole laser setup. To directly characterize its power stability and photodarkening effect, the fiber laser was kept at ∼2.1 kW for over 500 min with power degradation less than 1.1%. These results indicated that the all-gas-phase chelate precursor doping technique is highly competitive for Yb-APS fiber fabrication toward high-power laser, and the fabricated fiber is very suitable for 2 kW-level or above commercial fiber laser development.

With the boom of flexible electronic products and wearable devices, flexible energy storage devices, for example, supercapacitors with high performance, are attracting increasing interest. A flexible water-deactivated polyelectrolyte hydrogel electrolyte with good mechanical properties and high ionic conductivity was prepared by using an anionic polymer, carboxy methyl cellulose, and a cationic monomer, methacrylamidopropyltrimethyl ammonium chloride. It was then applied in a supercapacitor with flexible activated carbon electrodes. This flexible supercapacitor possesses a high operating voltage of 2.1 V owing to the low electrochemical activity for water within the hydrogel as a result of the 'molecular cages' effect and hydrophilic interactions between functional groups and surrounding water molecules. Furthermore, this supercapacitor exhibits good flexibility and tailorability. As the first example of water-deactivated polyelectrolyte hydrogel electrolytes in applications involving flexible high-voltage supercapacitors, this work provides a platform for the design of energy storage devices with high energy density for flexible and wearable electronic devices.

The large-scale synthesis accompanying structural modulation of efficient noble-metal-free catalysts with facile kinetics for the hydrogen evolution reaction (HER) is still a big challenge for electrolytic water splitting. Herein, we report a simple inkjet printing technology for the large-scale synthesis of a series of transition metal phosphide (TMP) nanoparticles encapsulated in N, P co-doped carbon supported on carbon fiber cloth (CF@NPC-TMP, TM = Mo, Co, Ni, Fe) as highly efficient hydrogen evolution cathodes using ionic liquids as phosphorus and carbon sources. The in-situ carbon nanolayers derived from ionic liquids not only expose abundant catalytically active sites and allow rapid electron transport to the catalytically active sites during HER but also effectively prevent the TMP nanoparticles from corroding to enhance their stability. All the as-prepared CF@NPC-TMP electrodes show ideal electrocatalytic performance for HER. Especially, the CF@NPC-MoP electrode only requires overpotentials of 87 and 145 mV to drive cathodic current densities of 10 and 100 mA cm−2 in 0.5 M H2SO4, respectively. In addition, this electrode continuously operates at a constant current density of 10 mA cm−2 for 20 h with negligible rise in operating potential. The resultant CF@NPC-TMP electrodes also show ideal electrocatalytic activities toward HER in alkaline and neutral media. Hence, the synthesis strategy developed in this study may spark interest in research on TMP-based nanomaterials for various applications.

To incorporate sufficient pumping power, a large-scale Yb-doped aluminophosphosilicate (Al2O3 -P2O5-SiO2, APS) fiber with 30- μ m core and 900- μ m inner clad in diameter, i.e., a 30/900 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Analyzed by an electron probe microanalyzer, the dopant concentration of Yb2O3, Al2O 3, and P2O5 was estimated to be 0.14 mol%, 1.1 mol%, and 1.4 mol%, respectively. Based on an all-fiberized master oscillator power-amplifier laser setup directly forward pumped by commercial 976-nm laser diodes, 6.85-kW laser output at 1079.79 nm was achieved with an optical-to-optical efficiency of 67.1%, and the beam factor of $M^{2}$ was 2.38. The results indicate that large-scale Yb-APS fiber is quite competitive for high-power fiber laser development.

By a chelate precursor doping technique, we designed and fabricated an ytterbium/cerium codoped aluminosilicate fiber for noticeable suppression of photodarkening and demonstrated its laser performance. Cerium/ytterbium ions ratio of 0.5 was specially designed to mitigate photodarkening. Aluminum/fluorine ions ratio of 1 was devised to keep low numerical aperture of fiber core. The measurements showed the fiber core was homogeneously doped with ~0.12 mol% Yb 2 O 3 , ~0.05 mol% Ce 2 O 3 , ~0.5 mol% Al 2 O 3 , and ~0.2 mol% SiF 4 , respectively. Tested in a master oscillator power amplifier system, the fiber presented 1930 W laser output power with optical-to-optical efficiency of 79.2%. Stabilized at 1850 W for over 500 min, the output power presented a relatively small power degradation of

Organosilane, with functional organic groups attached to inorganic silicon atoms, exhibits excellent passivation performance for pyrite. However, a considerable number of micro-cracks will gradually appear on the surface of passivation film under long-term corrosion of oxidizing medium, resulting in a significant decrease of passivation effect. To improve the stability and long-term performance of organosilane coating, a novel passivator (PT-ATP@HQ) with self-healing function was prepared to inhibit the oxidation of pyrite. We chose 3-mercaptopropyltrimethoxysilane (Prop-SH) and tetraethoxysilane (TEOS) as the host coating (PT), and attapulgite clay (ATP) loaded with 8-hydroxyquinoline (8-HQ) was used to endow the coating with better passivation and self-healing performance. The electrochemical and chemical leaching results showed that the addition of ATP@HQ greatly improved the passivation performance of PT coating. The passivation efficiencies of total Fe and SO42− reached to 88.1% and 79.2%, respectively. We also found that the protective capability of the scratched PT-ATP@HQ coating can be recovered automatically through 8-HQ release from ATP. The passivation and self-healing mechanisms were investigated by FT-IR, XPS, 29Si NMR, and other characterization methods, which were as follows: firstly, the organosilanes hydrolyzed to form highly active silanol groups, then dehydration condensation reaction occurred between silanol molecules and ATP@HQ to obtain cross-linked network structure connected by Si–O–Si bonds. After that, Si–OH groups reacted with the hydroxyl groups of pyrite to form Fe–O–Si bonds, thereby an inert and dense passivation film attached to the surface of pyrite. Once the passivation film is locally damaged, 8-HQ will automatically release to repair the cracks.

A common but important problem of carbon-based supercapacitors unresolved is the difficulty of achieving high specific capacitance over a wide voltage window when the electrodes are assembled into devices. Adjusting the structure of carbon materials is expected to tune the electrode potential and the surface charge density of the electrode materials, and thus further enhance the energy density of carbon-based supercapacitors. Herein, an efficient surface charge control strategy was developed to remarkably enhance the energy density of porous N, O codoped vertically aligned carbon nanosheets (VACNs) based solid-state symmetric supercapacitors through unzipping N, O codoped carbon tubes by transition metal atoms. Originating from the synergetic effect of vertically aligned structure and the doped N, O atoms, the assembled solid-state symmetric supercapacitor based on N, O codoped VACNs electrodes exhibits excellent electrochemical performance. The synthesis strategy may enlighten the design and fabrication ...

The coherent amplification network (CAN) aims at developing a laser system based on the coherent combination of multiple laser beams, which are produced through a network of high beam quality optical fiber amplifiers. For the front-end sources of high power laser facilities, single-mode linearly polarized beams in the nanosecond time scale are required. According to these two requirements, a millijoule polarized fiber laser system was studied. Using polarization maintaining Ytterbium-fiber laser system as the seed, 10-μm core diameter Yb-doped fiber amplifier as the first-stage power amplifier and 40-μm core diameter polarizing photonic crystal fiber (PCF) as the second-stage power amplifier, the all-fiber laser system output 1.06-mJ energy at 10 ns with diffraction limited mode quality. Using 85-μm core diameter rod-type PCF as the third-stage power amplifier, 2.5-mJ energy at 10-ns pulse width was obtained with better than 500:1 peak-to-foot pulse shaping ability and single-mode beam quality. The energy fluctuation of the system was 1.3% (rms) with 1-mJ output in an hour. This fiber laser system has the advantages of high beam quality, versatile pulse shaping ability, good stability, small volume, and free of maintenance, which can be used in many applications.

A series of organo-soluble six-membered ring copolyimides have been synthesized by one-step random copolymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) and 2,2′-bis(trifluormethyl)benzidine (BTFBz). The resulting copolyimides exhibit excellent thermal resistance (Tg > 450 °C) and fairly high storage moduli (5.7–7.1 GPa). XRD patterns suggest that they are amorphous and have large segmental distances (0.61–0.67 nm). The gas permeation properties of these copolyimide membranes and their five-membered ring analogue PMDA-TrMPD/BTFBz(1/1) (PMDA is the abbreviation of pyromellitic dianhydride, ‘1/1’ refers to molar ratio) are investigated. Among the NTDA-based copolyimide membranes, the gas permeability coefficient increases with an increase in the molar ratio of TrMPD to BTFBz. Moreover, except NTDA-TrMPD/BTFBz(3/1) the NTDA-based copolyimide membranes show significantly higher gas permeability coefficients and roughly similar ideal selectivities to the PMDA-TrMPD/BTFBz(1/1). For example, the NTDA-TrMPD/BTFBz(1/1) exhibits approximately one order of magnitude higher gas permeability coefficients but roughly similar selectivity values to that of PMDA-TrMPD/BTFBz(1/1) despite their exactly the same diamine composition. The NTDA-TrMPD/BTFBz(1/1) membrane exhibits excellent separation performance for CO2/CH4 (PCO2 = 930 Barrer, 1 Barrer = 1 × 10−10 cm3 (STP) cm−1 s−1 cm Hg−1; PCO2/PCH4 = 21.6) gas pair which almost reaches the latest upper bound reported by Robeson in 2008.

By using chelate precursor doping technique and traditional modified chemical vapor deposition system, we fabricated Yb-doped aluminophosphosilicate (Al2O3-P2O5-SiO2, ternary Yb-APS) large-mode-area fiber and reported on its laser performance. The fiber preform was doped with Al, P and Yb with concentration of ∼8000 ppm, ∼1700 ppm and ∼400 ppm in molar percent, respectively. Tested with master oscillator power amplifier system, the home-made Yb-APS fiber was found to present 1.02 kW at 1061.1 nm with a high slope efficiency of 81.2% and excellent laser stability with power fluctuation less than ±1.1% for over 10 h. Compared with Yb-doped aluminosilicate (Al2O3-SiO2, binary Yb-AS) fiber, the introduction of P2O5 effectively suppressed photodarkening effect even the P/Al ratio is much less than 1, indicating that Yb-APS fiber is a better candidate for high power fiber lasers.

The practical application of high energy lithium-sulfur batteries is still limited by unstable lithium anodes and the shuttle effect of polysulfides. Herein, a gel-like electrolyte induced by fumed alumina is proposed for dendrite-free Li deposition, lower over-potential and better cycle stability. Li-S@pPAN cells with the proposed electrolyte exhibit outstanding cycle stability and rate performance with capacity retentions of 95.1% after 300 cycles and 76.5% at 10C against 1C, respectively.

The strategy of compatibly integrating cost-effective HER- and OER-active materials in a well-designed manner is expected to obtain bifunctional electrocatalysts for overall water splitting. We extend this strategy to a bifunctional self-supported electrode for water splitting to achieve a dynamic balance between the HER and OER through a fast, simple and economical fabrication process. The electrocatalytic activities of the self-supported multiphase NiS–NiS2–Ni3S2/NF (m-NiSx/NF) electrodes toward water splitting are obtained and optimized by modulating the quantity of sulfur powder during the reaction procedure. As a result, the self-supported m-NiSx-0.5/NF electrode exhibits overpotentials of 143 mV and 137 mV to afford a current density of 20 mA cm−2 for the OER and HER in 1.0 M KOH aqueous solution, respectively. Impressively, overall water splitting with 10 mA cm−2 at a low voltage of 1.46 V is achieved using self-supported m-NiSx-0.5/NF as both the anode and cathode electrodes, surpassing the performance of nearly all the recently reported nonprecious electrocatalysts for overall water splitting.

Quantum defect originating from the stimulated Raman scattering (SRS) effect is a heat source that induces refractive index grating and, thus, significantly decreases the threshold of transverse mode instability (TMI), which is the main limiting factor for the power scaling of high-power fiber lasers. A semi-analytical model that takes the TMI and SRS effects into account was developed, and the impact of the Raman content variation due to changes in the injected seed and fiber length on the TMI threshold was investigated. Experimental demonstrations of the impact of the SRS effect on the TMI threshold are presented. We proved that TMI affects the beam quality of the signal light rather than the Raman light. Taking these facts into account, the suppression of SRS could be an effective way to counter the TMI of fiber lasers.

In this paper, we present a 10 kW-level output power fiber amplifier based on tandem-pumping. The characteristics of active fiber for amplifier stage is reported. To ensure adequate absorption of tandem pumping light in relatively short fiber length, a large-scale Yb3+ doped aluminophosphosilicate (Al2O3-P2O5-SiO2, APS) fiber with 50 μm core and 400 μm inner-clad in diameter, i.e., a 50/400 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combined with chelate precursor doping technique. The measurements showed that the dopant concentration of Yb2O3, Al2O3, and P2O5 was estimated to be 0.17 mol%, 1.4 mol%, and 1.5 mol%, respectively, and the absorption coefficient of the fiber was about 0.77 dB/m at 1018 nm. The amplifier stage with this 40 m Yb-APS fiber tandem-pumped by 1018 nm fiber laser, delivered 9.82 kW laser output at 1080.08 nm with an optical-to optical efficiency of 86.8%. The knowledge of the characteristics of the Yb3+ doped APS fiber can usefully guide future design of high output power fiber amplifier based on tandem pumping.

It is a critical issue to reduce the thermal conductivity and increase the thermal expansion coefficient of ceramic thermal barrier coating (TBC) materials in the course of their utilization. To synthesize samples with different composition and measure their thermal conductivity by the traditional experimental approaches is time-consuming and expensive. Most classic and empirical models work inefficiently and inaccurately when researchers attempt to predict the thermophysical properties of TBC materials. In this research project, we tentatively exploit a Genetic Algorithm-Support Vector Regression (GA-SVR) machine learning model to study the thermophysical properties, illustrated with the potential TBC materials ZrO2 doped DyTaO4, which has resulted in the lowest thermal conductivity in rare earth tantalates RETaO4 system. Meanwhile, we employ statistical parameters of correlation coefficient (R2) and mean square error (MSE) to evaluate the accuracy and reliability of the model. The results reveal that this model has brought about high correlation coefficients of thermal conductivity and thermal expansion coefficient (99.8% and 99.9%, respectively), while the MSE values are 0.00052 and 0.00019, respectively. The doping concentration of ZrO2 was optimized to reach as low as 0.085–0.095, so as to reduce their thermal conductivity further and increase their thermal expansion. This model provides an accurate and reliable option for researchers to design ceramic thermal barrier coating materials.

The results of a commissioning experiment on the SILEX-Ⅱ laser facility (formerly known as CAEP-PW) are reported. SILEX-Ⅱ is a complete optical parametric chirped-pulse amplification laser facility. The peak power reached about 1 PW in a 30 fs pulse duration during the experiment. The laser contrast was better than 1010 at 20 ps ahead of the main pulse. In the basic laser foil target interaction, a set of experimental data were collected, including spatially resolved x-ray emission, the image of the coherent transition radiation, the harmonic spectra in the direction of reflection, the energy spectra and beam profile of accelerated protons, hot-electron spectra, and transmitted laser energy fraction and spatial distribution. The experimental results show that the laser intensity reached 5 × 1020 W/cm2 within a 5.8 µm focus (FWHM). Significant laser transmission did not occur when the thickness of the CH foil was equal to or greater than 50 nm. The maximum energy of the accelerated protons in the target normal direction was roughly unchanged when the target thickness varied between 50 nm and 15 µm. The maximum proton energy via the target normal sheath field acceleration mechanism was about 21 MeV. We expect the on-target laser intensity to reach 1022 W/cm2 in the near future, after optimization of the laser focus and upgrade of the laser power to 3 PW.

Devising and facilely synthesizing an efficient noble metal-free electrocatalyst for the acceleration of the sluggish kinetics in the hydrogen-evolution reaction (HER) is still a big challenge for electrolytic water splitting. Herein, we present a simple one-step approach for constructing self-supported biocarbon-fiber cloth decorated with molybdenum carbide nanoparticles (BCF/Mo2C) electrodes by a direct annealing treatment of the Mo oxyanions loaded cotton T-shirt. The Mo2C nanoparticles not only serve as the catalytic active sites toward the HER but also enhance the hydrophilicity and conductivity of resultant electrodes. As an integrated three-dimensional HER cathode catalyst, the BCF/Mo2C exhibits outstanding electrocatalytic performance with extremely low overpotentials of 88 and 115 mV to drive a current density of 20 mA cm–2 in alkaline and acidic media, respectively. In addition, it can continuously work for 50 h with little decrease in the cathodic current density in both alkaline and acidic sol...

We fabricated and reported on an Yb-doped aluminophosphosilicate fiber for tandem pumping scheme by 1018nm fiber laser. 9.82 kW laser output at 1080 nm with an optical-to-optical efficiency of 86.8% was achieved with this fiber amplifier. © 2020 The Author(s)

An approach to fabricate cladding mode stripping device with ultra high power handling capability is presented, which can strip the cladding power gradually and avoid local overheating. Removed pump power up to 2.16 kW was experimentally demonstrated for the first time, delivering an attenuation of 21.7 dB with highest temperature being 55 °C at a room temperature of 20°C.

The photodarkening losses of Al/Yb-doped fiber, Al/P/Yb-doped fiber and Al/Ce/Yb-doped fiber were 181.82 dB/m, 84.56 dB/m, 49.65 dB/m, respectively. The result shows the photodarkening loss can be markedly suppressed by codoping with Ce and P.

An all-fiber supercontinuum source with 215 W of average power and spectra spanning from 480 nm to over 2000 nm is reported. Constructed with a pulsed seed and four stages of amplifiers based on large-mode-area fiber for mitigating nonlinear effects, the pump power of supercontinuum is up scaled to 556 W. A special designed mode field adaptor is developed to maximize the coupling of pump to photonic crystal fiber for improving the power scaling capability of supercontinuum generation. In the end, the main factors influencing the conversion efficiency are also discussed.

Mode instability with different mode excitation has been investigated by off-splicing the fusion point in a 4 kW-level monolithic fiber laser system, which reveals that the fiber systems exciting more high order mode content exhibits lower beam quality but higher mode instability threshold. The static-to-dynamic mode degradation and dynamic-only mode degradation have also been observed in the same high power fiber amplifier by varying the mode excitation, which implicates that the mode excitation plays an important role in mode characteristics in high power fiber lasers. By employing a seed with near fundamental mode beam quality, only dynamic mode degradation-mode instability sets in with negligible static beam quality degradation. Then the fusion point in the seed laser is offset spliced to excite high order mode. As the output power of the main amplifier scales, the beam quality degrades with the beam profile being static, and then the dynamic mode instability sets in, the power threshold of which is higher than that with good beam quality seed. We consider that the static mode degradation is caused by the presence of incoherent supposition of fundamental and high order mode, which leads to that the measured dynamic mode instability threshold is higher.

In this paper, we report a 3.7 kW all fiber narrow linewidth single mode fiber laser. The full width at half-maximum is about 0.30 nm, and the beam quality is Mx2=1.358, My2=1.202 at maximum output power. The laser is achieved by simultaneously suppressing nonlinear effects and mode instability (MI). Different seeds are injected into the main amplifier to study stimulated Raman scattering (SRS) effect. The results show that the phase modulated single frequency seed is benefit to suppress the SRS effect. For the phase modulated single frequency seed, inserting a filter in preamplifier will suppress amplified spontaneous emission (ASE) and decrease the backward power. By optimizing the coiling of active fiber, the MI effect is suppressed.

A high-power monolithic continuous-wave fiber amplifier at 1064 nm has been demonstrated based on a piece of confined ytterbium-doped fiber, which generated 3.5 kW narrow-linewidth laser with near-diffraction-limited beam quality. By tailoring the diameter of gain dopant across the fiber core, and optimizing the profile of refractive index and doping concentration, the confined doping fiber works making the fundamental mode more dominant in transverse mode competition, while suppressing the high-order mode. In a kilowatt-level narrow-linewidth fiber master oscillator power amplifier (MOPA) system, the threshold of mode instability (MI) is about 2.2 times as much as that of the conventional fiber amplifier. Then, by increasing seed power and utilizing a MOPA configuration with four amplifier stages, up to 3.57 kW signal output, a slope efficiency of 61% without any sign of MI or stimulated Raman scattering for a spectral dynamic range of higher than − 50 d B is obtained. A further increase of the output power was only limited by the available laser-diode pump power. To the best of our knowledge, this is the highest narrow-linewidth laser power generated from the confined doping monolithic fiber amplifier.

The anisotropies of mechanics and thermodynamics properties of zirconia with three zero-pressure polymorphs were studied by using first-principles calculations. It has been shown that Young’s moduli of three phases strongly depend on directions. The sound velocities of faster mixed mode ( v + ) is much larger than that of slower mixed mode ( v − ) and pure transverse mode ( v t ) in monoclinic phase. For both tetragonal phase and the cubic phase, most pure longitudinal mode ( v l ) have the greatest sound velocity among the three acoustic modes. According to the Clarke's model, three zero-pressure polymorphs zirconia also have pronounced anisotropic minimum thermal conductivity.

Exploring environmentally friendly, efficient and recyclable heterogeneous catalysts for organic reactions in aqueous media is important for the development of green and sustainable processes. In this work, an amphiphilic porous organic polymer supported palladium catalyst (Pd@UPOP) was synthesized via a facile urea-forming condensation of commercially available 3,3′-diaminobenzidine and 1,4-phenylene diisocyanate, followed by immobilizing palladium acetate at room temperature. Physico-chemical characterization suggested that the obtained material possessed a good porous structure and amphiphilic properties. Aminocarbonylation of aryl iodides with amines in water showed that Pd@UPOP is more active than previously reported heterogeneous palladium catalysts. Under balloon pressure of carbon monoxide, a palladium catalyst loading as low as 0.5 mol% was sufficient for a 98% yield of N,N-diethylbenzamide in the model reaction, corresponding to a high turnover frequency of 98 h−1. The catalyst could be used for at least five consecutive runs with the catalytic activity being recovered easily after simple manipulations.

By using modified chemical vapor deposition system combined with chelate precursor doping technique, we report on the fabrication and characterization of Yb-doped aluminophosphosilicate (Al2O3-P2O 5-SiO2) laser fiber. Based on a master oscillator power amplifier laser setup and pumped directly by 976 nm laser diodes, 3.1 kW laser at ∼1064 nm was achieved with a slope efficiency of 78.4%. Benefiting from codoped Al and P, the laser output power showed no evidence of roll-over. The linear fitting of the output power versus the pump power shows the potentiality for further power scaling. The results indicate that chelate precursor doping technique is a competitive method for rare-earth-ion-doped fiber preform fabrication, and aluminophosphosilicate host material has potentiality to develop multi-kW level laser fibers.

We demonstrate for the first time how to assemble mechanized hollow zirconia nanospheres (MHzNs), consisting of hollow mesoporous zirconia nanospheres (HMZNs) as nanoscaffolds and supramolecular switches anchored on the exterior surface of HMZNs. The remarkable advantage of substitution of HMZNs for conventional mesoporous silica nanoscaffolds is that HMZNs can suffer the hot alkaline reaction environment, which provides a novel strategy for functionalization and thus achieve dual pH-mediated controlled release functions by simple and practicable assembly procedure. Under neutral solution, cucurbituril[7] (CB[7]) macrocycles complexed with propanone bis(2-aminoethyl)ketal (PBAEK) to form [2]pseudorotaxanes as supramolecular switches, blocking the pore orifices and preventing the undesirable leakage of cargoes. When solution pH was adjusted to alkaline range, CB[7] macrocycles, acting as caps, disassociated from PBAEK stalks and opened the switches due to the dramatic decrease of ion-dipole interactions. While under acidic conditions, PBAEK stalks were broken on account of the cleavage of ketal groups, resulting in the collapse of supramolecular switches and subsequent release of encapsulated cargoes. MHzNs owning dual pH-mediated controlled release characteristic are expected to apply in many fields. In this work, the feasibility of doxorubicin (DOX)-loaded MHzNs as targeted drug delivery systems was evaluated. In vitro cellular studies demonstrate that DOX-loaded MHzNs can be easily taken up by SMMC-7721 cells, can rapidly release DOX intracellularly, and can enhance cytotoxicity against tumor cells, proving their potential for chemotherapy.

The diluent NaCl was introduced into the WO 3 -Mg-C-Na 2 CO 3 system to prepare submicron tungsten carbide (WC) powders via salt-assisted combustion synthesis. The products were analyzed by SEM, EDS and XRD, and the effects of C content on morphology, average particle size and phase composition of the products were studied. Results show that on basis of the m = 0.125 (the number of moles of Na 2 CO 3 ), when the number of moles of carbon in raw material increases from l =2 to 2.25 and 2.5, before leaching, the product is made up of a small number of large size particles and a large number of small size particles; after leaching, samples are composed of aggregates of submicron particles, and the sintering phenomenon between particles is very weak, indicating low degree of aggregation. Particle size distribution of leached product almost falls into the normal distribution, and the particle sizes range from 200 nm to 350 nm. Under the condition of l =2.25, a main target product is WC, and the content of by-products W 2 C is extremely few. That is, k = 2.0 (the number of moles of NaCl), m = 0.125, and l =2.25 are the process conditions for single-phase WC synthesis.

To consider both high-power handling and blue-extended supercontinuum (SC) generation, a long-tapered photonic crystal fiber is pumped by a high-power laser source. An SC ranging from 390 to 2400 nm with 314.7 W output power is obtained. A spectral component below 960 nm accounts for 36.1% of the total output power, exceeding 113.5 W, with a spectral flatness within 16 dB. To the best of our knowledge, this is the first time an SC coverage of all visible wavelengths with more than 300 W output power has been achieved. This result increases the output power of the SC covering the visible range by a factor of three.

A microwave photonic frequency mixer constituted of an optically-carried local oscillator (LO) and a wavelength-division modulator was proposed. The wavelength-division modulator chip, which was consisted of a silicon phase modulator, two micro-ring filters, a photodetector, two optical couplers, and two grating couplers, was designed and fabricated. Based on the chip, a microwave photonic harmonic frequency mixer was implemented. In the experiment, an optically-carried LO was generated by double-sideband suppressed-carrier modulation at a Mach-Zehnder modulator. An RF signal from 6 to 16 GHz was successfully converted into a signal with a frequency of 33 to 23 GHz. In order to suppress the remaining mixing spurs, two solutions, i.e., increasing the rejection ratio of the micro-ring filter to decrease the intensity of the leaked optically-carried LO and introducing an optical phase shifter to correct the phase of the leaked optically-carried LO, were proposed and verified by simulation. It should be noted that the latter is simpler and more suitable for photonic integration.

In this paper, the alumina was fusion welded by femtosecond laser. The levels of each parameter were firstly optimized by monofactor analysis method. Then the complex influences of laser parameters on the weld bead geometry were clarified by Taguchi’s approach. The range analysis was used to study the significance of the process parameters on the joint size and the variance analysis were used to clarify the influence of the experimental error. The results show that a crack free Al2O3 femtosecond laser welded joint with dense ripple on the surface is obtained when the process parameters are selected reasonable. The influence degree of three factors on weld width was defocusing distance, laser power and welding speed in turns. The influence degree of three factors on weld penetration was welding speed, laser power and defocusing distance in turns. The maximum weld width and penetration is 205um and 909um, respectively. The minimum weld width and penetration is 26um and 140 um, respectively.

Laser pulses of 200 ps with extremely high intensities and high energies are sufficient to satisfy the demand of shock ignition, which is an alternative path to ignition in inertial confinement fusion (ICF). This paper reports a type of Brillouin scheme to obtain high-intensity 200-ps laser pulses, where the pulse durations are a challenge for conventional pulsed laser amplification systems. In the amplification process, excited Brillouin acoustic waves fulfill the nonlinear optical effect through which the high energy of a long pump pulse is entirely transferred to a 200-ps laser pulse. This method was introduced and achieved within the SG-III prototype system in China. Compared favorably with the intensity of $2~\text{GW}/\text{cm}^{2}$ in existing ICF laser drivers, a 6.96- $\text{GW}/\text{cm}^{2}$ pulse with a width of 170 ps was obtained in our experiment. The practical scalability of the results to larger ICF laser drivers is discussed.