This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature fi...This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.展开更多
We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr^(4+):YAG composite medium monolithic laser with four-beam output. The energy of a laser pu...We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr^(4+):YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 m J with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics.展开更多
This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology (especially the shape) and, consequently, density and compression properties of in si...This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology (especially the shape) and, consequently, density and compression properties of in situ Ti-TiB composite materials produced by selective laser melting (SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium (CP-Ti) and 5 wt% titanium diboride (TiB2) powders and subsequently milled for two different times (i.e. 2 h and 4 h). The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti-TiB composite samples prepared from 2 h and 4 h milled Ti-TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those (883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density (i.e. increasing porosity level) of the Ti-TiB composite materials and their mechanical properties.展开更多
In this work, new plain and composite high-energy solitons of the cubic–quintic Swift–Hohenberg equation were numerically found. Starting from a composite pulse found by Soto-Crespo and Akhmediev and changing some p...In this work, new plain and composite high-energy solitons of the cubic–quintic Swift–Hohenberg equation were numerically found. Starting from a composite pulse found by Soto-Crespo and Akhmediev and changing some parameter values allowed us to find these high energy pulses. We also found the region in the parameter space in which these solutions exist. Some pulse characteristics, namely, temporal and spectral profiles and chirp, are presented. The study of the pulse energy shows its independence of the dispersion parameter but its dependence on the nonlinear gain. An extreme amplitude pulse has also been found.展开更多
USLNG CO<sub>2</sub> laser beam as a heat source to sinter whole P/M (powder metallurgy) green com-pact is a new technique. As reported in refs. [1--4], the advantages of the laser sintering ofCu-base an...USLNG CO<sub>2</sub> laser beam as a heat source to sinter whole P/M (powder metallurgy) green com-pact is a new technique. As reported in refs. [1--4], the advantages of the laser sintering ofCu-base and Fe-base green compact were characterized by rapid sintering rate, no contamina-tion, fine structure and good properties.展开更多
Fe-based composite coatings were fabricated on 5 CrNiMo die steel by laser beam melting a precursor mixture of ferrotitanium,ferrochromium,ferromolybdenum,B4 C and Y2 O3 powders.Micro structure and properties of the c...Fe-based composite coatings were fabricated on 5 CrNiMo die steel by laser beam melting a precursor mixture of ferrotitanium,ferrochromium,ferromolybdenum,B4 C and Y2 O3 powders.Micro structure and properties of the coatings were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectrometer(EDS),resistance furnace and high-temperature tribometer.The results show that(Ti,Mo)C particles with flower-like and(Ti,Mo)B2 with block-like shapes are in situ formed during laser cladding.Volume faction of multiple ceramic particles increases with the increasing of Y2 O3.The cumulative oxidation mass of the coating with 2 wt% Y2 O3 is decreased by one-third than that of the coating without Y2 O3.The oxidation layer of the coating with Y2 O3 is getting smooth.Meanwhile,high temperature wear volume loss of the coating with 2 wt% Y2 O3 is about 40% that of the coating without Y2 O3.The coating with 2 wt% Y2 O3 shows a smoother wear scar and few flat grooves are observed after high temperature wear test.展开更多
Carbon materials are widely used for supercapacitor applications thanks to their high surface area, good rate capability, and excellent cycling stability. However, the development of high energy density carbon superca...Carbon materials are widely used for supercapacitor applications thanks to their high surface area, good rate capability, and excellent cycling stability. However, the development of high energy density carbon supercapacitors still remains a challenge. In this work, hollow Co3O4 nanoboxes have been embedded into three-dimensional macroporous laser-scribed graphene (LSG) to produce composite electrodes with improved electrochemical performance. Here, Co3O4 provides high capacity through fast and reversible redox reactions, while LSG serves as a conductive network to maintain high power. The open nanobox morphology is a unique solution for extracting the maximum capacity from Co3O4, resulting in electrodes whose surfaces, both internal and external, are accessible to the electrolyte. The electrochemical performance of the composite material is promising with a volumetric capacity of 60.0 C/cm^3 and a specific capacity of 542.3 C/g, corresponding to 682.0 C/g of the constituent Co3O4. With a low equivalent series resistance of 0.9 Ω, the Co3O4/LSG electrode is able to maintain 113.1% of its original capacity after 10,000 cycles. This work provides new insights into the design of high-performance carbon/metal oxide nano- composites for next-generation energy storage devices.展开更多
The surface of Ni_(61)Nb_(39) crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the to...The surface of Ni_(61)Nb_(39) crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the top surface under optimal parameters.An amorphous-crystalline composite layer with the depth from 10 to 50μm,consisting of amorphous matrix and intermetallic phases of Ni_3 Nb and Ni_6Nb_7,could be formed.The micro-hardness(about 831HV)of the treated surface was remarkably improved by nearly 100% compared with the value of the crystalline substrate caused by the formation of the fully amorphous structure.A finite volume simulation was adopted to evaluate the temperature distribution in the laser-affected zone of Ni_(61)Nb_(39) alloys and to reveal the mechanism of glass formation in the laser-affected zone.展开更多
文摘This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.
基金Autoritatea Nationala pentru Cercetare Stiintifica(ANCS)(PN-II-PT-PCCA-2011-3.2-1040(58/2012),NUCLEU4N/2016)Horizon 2020(691688 LASIG-TWIN)
文摘We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr^(4+):YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 m J with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics.
基金supported by the Australian Research Council’s Projects Funding Scheme (No. DP110101653)the European Commission (BioTiNet-ITN G.A. No.264635)the Deutsche Forschungsgemeinschaft (SFB/Transregio 79, Project M1)
文摘This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology (especially the shape) and, consequently, density and compression properties of in situ Ti-TiB composite materials produced by selective laser melting (SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium (CP-Ti) and 5 wt% titanium diboride (TiB2) powders and subsequently milled for two different times (i.e. 2 h and 4 h). The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti-TiB composite samples prepared from 2 h and 4 h milled Ti-TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those (883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density (i.e. increasing porosity level) of the Ti-TiB composite materials and their mechanical properties.
基金FCT(Fundacao para a Ciência e Tecnologia)for supporting this work through the Project UID/CTM/50025/2013
文摘In this work, new plain and composite high-energy solitons of the cubic–quintic Swift–Hohenberg equation were numerically found. Starting from a composite pulse found by Soto-Crespo and Akhmediev and changing some parameter values allowed us to find these high energy pulses. We also found the region in the parameter space in which these solutions exist. Some pulse characteristics, namely, temporal and spectral profiles and chirp, are presented. The study of the pulse energy shows its independence of the dispersion parameter but its dependence on the nonlinear gain. An extreme amplitude pulse has also been found.
文摘USLNG CO<sub>2</sub> laser beam as a heat source to sinter whole P/M (powder metallurgy) green com-pact is a new technique. As reported in refs. [1--4], the advantages of the laser sintering ofCu-base and Fe-base green compact were characterized by rapid sintering rate, no contamina-tion, fine structure and good properties.
基金the Natural Science Foundation of Shandong Province(ZR2017MEE021),China。
文摘Fe-based composite coatings were fabricated on 5 CrNiMo die steel by laser beam melting a precursor mixture of ferrotitanium,ferrochromium,ferromolybdenum,B4 C and Y2 O3 powders.Micro structure and properties of the coatings were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectrometer(EDS),resistance furnace and high-temperature tribometer.The results show that(Ti,Mo)C particles with flower-like and(Ti,Mo)B2 with block-like shapes are in situ formed during laser cladding.Volume faction of multiple ceramic particles increases with the increasing of Y2 O3.The cumulative oxidation mass of the coating with 2 wt% Y2 O3 is decreased by one-third than that of the coating without Y2 O3.The oxidation layer of the coating with Y2 O3 is getting smooth.Meanwhile,high temperature wear volume loss of the coating with 2 wt% Y2 O3 is about 40% that of the coating without Y2 O3.The coating with 2 wt% Y2 O3 shows a smoother wear scar and few flat grooves are observed after high temperature wear test.
文摘Carbon materials are widely used for supercapacitor applications thanks to their high surface area, good rate capability, and excellent cycling stability. However, the development of high energy density carbon supercapacitors still remains a challenge. In this work, hollow Co3O4 nanoboxes have been embedded into three-dimensional macroporous laser-scribed graphene (LSG) to produce composite electrodes with improved electrochemical performance. Here, Co3O4 provides high capacity through fast and reversible redox reactions, while LSG serves as a conductive network to maintain high power. The open nanobox morphology is a unique solution for extracting the maximum capacity from Co3O4, resulting in electrodes whose surfaces, both internal and external, are accessible to the electrolyte. The electrochemical performance of the composite material is promising with a volumetric capacity of 60.0 C/cm^3 and a specific capacity of 542.3 C/g, corresponding to 682.0 C/g of the constituent Co3O4. With a low equivalent series resistance of 0.9 Ω, the Co3O4/LSG electrode is able to maintain 113.1% of its original capacity after 10,000 cycles. This work provides new insights into the design of high-performance carbon/metal oxide nano- composites for next-generation energy storage devices.
基金Item Sponsored by National Natural Science Foundation of China(51131002,51301196)Fundamental Research Funds for the Central Universities of China(YWF-15-CLXY-002)Fok Ying Tong Education Foundation of China(142008)
文摘The surface of Ni_(61)Nb_(39) crystalline ingot was treated by laser surface melting with different processing parameters.A fully amorphous layer with a thickness of approximately 10μm could be produced on the top surface under optimal parameters.An amorphous-crystalline composite layer with the depth from 10 to 50μm,consisting of amorphous matrix and intermetallic phases of Ni_3 Nb and Ni_6Nb_7,could be formed.The micro-hardness(about 831HV)of the treated surface was remarkably improved by nearly 100% compared with the value of the crystalline substrate caused by the formation of the fully amorphous structure.A finite volume simulation was adopted to evaluate the temperature distribution in the laser-affected zone of Ni_(61)Nb_(39) alloys and to reveal the mechanism of glass formation in the laser-affected zone.