共查询到20条相似文献,搜索用时 390 毫秒
1.
Brannerite MnV 2 O 6 with plate-like shape is successfully synthesized by hydrothermal method.Its crystal structure and morphology are investigated by x-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscope (TEM),high resolution transmission electron microscopy (HRTEM) and select area electronic diffraction (SAED).The results show that the brannerite MnV 2 O 6 with monoclinic structure has a uniform plate-like shape with a diameter of about 5-8 μm and a thickness of about 500 nm.SAED patterns further confirm the structure of the brannerite MnV 2 O 6 and the single crystalline character of the plate crystal.Magnetic properties are measured by superconducting quantum interference device (SQUID) in a temperature range of 2-300 K under a magnetic field of 1 T.The magnetic measurement results indicate that the material undergoes an antiferromagnetic transition with a N’eel temperature of 17 K.Above 50 K,the inverse susceptibility is fitted well to the Curie-Weiss law with a calculated moment of 5.98 μ B.Finally,the origin of antiferromagnetic behaviour in the brannerite MnV 2 O 6 is explained by means of Anderson model. 相似文献
2.
KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries (e.g., width, morphology, and depth of defects) are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 μ. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μ for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects. 相似文献
3.
Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal 下载免费PDF全文
This paper reports that the Tm^3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The roomtemperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Ω2=9.3155×10^-20 cm^2, Ω4=8.4103×10^-20 cm^2, Ω6=1.5908×10^-20 cm^2, the fluorescence lifetime is calculated to be 2.03 ms for ^3F4 → ^3H6 transition, and the integrated emission cross section is 5.81×10^-18 cm^2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuouswave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06μm with spectral bandwidth of -13.6 nm. 相似文献
4.
Judd-Oflet analysis of spectrum and laser performance of Ho:YAP crystal end-pumped by 1.91μm Tm:YLF laser 下载免费PDF全文
The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm. 相似文献
5.
6.
High quality Ge was epitaxially grown on Si using ultrahigh
vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates
efficient germanium-on-silicon p-i-n photodetectors with 0.8~μm
Ge, with responsivities as high as 0.38 and 0.21~A/W at 1.31 and
1.55~μ m, respectively. The dark current density is
0.37~mA/cm2 and 29.4~mA/cm2 at 0~V and a reverse bias of
0.5~V. The detector with a diameter of 30~μ m, a
3~dB-bandwidth of 4.72~GHz at an incident wavelength of 1550~nm and
zero external bias has been measured. At a reverse bias of 3~V, the
bandwidth is 6.28~GHz. 相似文献
7.
High efficiency and broad bandwidth grating coupler between nanophotonic waveguide and fibre 下载免费PDF全文
A high efficiency and broad bandwidth grating coupler
between a silicon-on-insulator (SOI) nanophotonic waveguide and fibre
is designed and fabricated. Coupling efficiencies of 46\% and
25\% at a wavelength of 1.55~μ m are achieved by simulation
and experiment, respectively. An optical 3~dB bandwidth of 45~nm
from 1530~nm to 1575~nm is also obtained in experiment. Numerical
calculation shows that a tolerance to fabrication error of 10~nm
in etch depth is achievable. The measurement results indicate that
the alignment error of ±2~μ m results in less than 1~dB
additional coupling loss. 相似文献
8.
The transmission enhancement of a THz pulse through an Ag/Ag2O layer detected by terahertz time-domain spectroscopy 下载免费PDF全文
This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS (time-domain spectroscopy). As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500μm-GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening. 相似文献
9.
The absorption and emission spectra of the YVO4 single crystal co-doped with 1 at.% Nd^3+ and 1 at.% Yb^3+ are investigated. The efficient Nd^3+ → Yb^3+ energy transfer and the back transfer (Yb^3+ → Nd^3+) are observed at room temperature. The fluorescence lifetime of the 4F3/2 level of Nd^3+ in Nd,Yb:YVO4 is measured under 808 nm laser light excitation. The efficiency of Nd^3+ → Yb^3+ energy transfer in YVO4 is determined to be about 34%. 相似文献
10.
A chemical vapour deposition (CVD) diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo (MC) simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection. 相似文献
11.
Simulated human eye retina adaptive optics imaging system based on a liquid crystal on silicon device 下载免费PDF全文
In order to obtain a clear image of the retina of model eye, an
adaptive optics system used to correct the wave-front error is
introduced in this paper. The spatial light modulator that we use
here is a liquid crystal on a silicon device instead of a
conversional deformable mirror. A paper with carbon granule is used
to simulate the retina of human eye. The pupil size of the model eye
is adjustable (3--7mm). A Shack-Hartman wave-front sensor is used
to detect the wave-front aberration. With this construction, a value
of peak-to-valley is achieved to be 0.086Λ, where
Λ is wavelength. The modulation transfer functions before
and after corrections are compared. And the resolution of this
system after correction (69lp/m) is very close to the diffraction
limit resolution. The carbon granule on the white paper which has a
size of 4.7μm is seen clearly. The size of the retina cell is
between 4 and 10μm. So this system has an ability to image
the human eye's retina. 相似文献
12.
Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4+ charge transfer transition 下载免费PDF全文
Ce^4+-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4+ ions doped in Ca2SnO4 occupy the Sn^4+ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime (-83μs) for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4+ charge transfer (CT). The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4+ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration (x - 0.03) is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%. 相似文献
13.
The transmissions of oxygen ions through Al2O3 nanocapillaries each 50 nm in diameter and 10 μm in length at a series of different tilt angles are measured,where the ions with energies ranging from 10 to 60 keV and charge states from 1 up to 6 are involved.The angular distribution and the transmission yields of transported ions are investigated.Our results indicate both the existence of a guiding effect when ions pass through the capillary and a significant dependence of the ion transmission on the energy and the charge state of the ions.The guiding effects are observed to be enhanced at lower projectile energies and higher charge states.Meanwhile,the results also exhibit that the transmission yields increase as the tilt angle decreases at a given energy and charge state. 相似文献
14.
Application of sampled grating to control the lasing wavelength in complex-coupled DFB laser 下载免费PDF全文
This paper reports that the complex-coupled distributed feedback
laser with the sampled grating has been designed and fabricated. The
+1st order reflection of the sampled grating is utilized for
laser single mode operation, which is 1.5387~μ m in the
experiment. The typical threshold current of the device is 30~mA,
and the optical output power is about 10~mW at the injection current
of 100~mA. 相似文献
15.
Ho^3+ : GdVO4 is a new laser material suitable for high-power laser systems. In this paper we measure the absorption spectra of Ho^3+ in the sample Ho^3+: GdVO4. The intensity parameters are calculated by using the Judd-Ofelt theory. Some predicted spectroscopic parameters, such as the spontaneous radiative transition rate, branching ratio and integrated emission cross section are dealt with. And we also compare the optical parameters with those of other materials. From these results, it is found that there are many transitions which have large oscillator strengths and large integrated emission cross sections. Especially the transitions such as ^5 F4 → ^5 I 8, ^5 S2→^5 I8, ^5 F5 → ^5 I8 and ^5 I7 →^ 5 I8 are useful in solid-state lasers and other fields. Finally, we discuss the splitting of the energy levels of Ho^3+ in the crystal GdVO4 based on the group theory. 相似文献
16.
Guiding of 150 keV O6+ ions through nanocapillaries in an uncoated Al2O3 membrane: special time dependence of the transmission profile width 下载免费PDF全文
<正>This paper reports that the transmission of O6+ ions with energy of 150keV through capillaries in an uncoated Al2O3 membrane was measured,and agreements with previously reported results in general angular distribution of the transmitted ions and the transmission fractions as a function of the tilt angle well fitted to Gaussian-like functions were observed.Due to using an uncoated capillary membrane,ourψc is larger than that using a gold-coated one with a smaller value of(?),which suggests a larger equilibrium charge Q∞in our experiment.The observed special width variation with time and a larger width than that using a smaller(?) were qualitatively explained by using mean-field classical transport theory based on a classical-trajectory Monte Carlo simulation. 相似文献
17.
The structure and magnetic properties of Y2Fe16Al compound have been investigated by means of x-ray diffraction and magnetization measurements. The Y2Fe Fe16Al compound has a hexagonal Th$_{2}$Ni$_{17}$-type structure. Negative thermal expansion was found in Y2Fe16Al compound in the temperature range from 332 to 438K by x-ray dilatometry. The coefficient of the average thermal expansion is \alpha =-3.4\times 10-5K-1. The spontaneous magnetostrictive deformations from 293 to 427K have been calculated based on the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation \textit{$\omega $}$_{\rm S}$ decreases from 5.4$\times $10-3to near zero with temperature increasing from 293 to 427K, the spontaneous linear magnetostrictive deformation \textit{$\lambda $}$_{\rm c}$ along the $c$ axis is much larger than the spontaneous linear magnetostrictive deformation \textit{$\lambda $}$_{\rm a}$ in basal-plane in the same temperature range except near 427K. 相似文献
18.
Magnetic properties and magnetocaloric effects of
Tb6Co1.67Si3 have been investigated by magnetization
measurement. This compound is of a hexagonal
Ce$_{6}$Ni$_{2}$Si$_{3}$-type structure with a saturation
magnetization of 187\,emu/g at 5\,K and a reversible second-order
magnetic transition at Curie temperature $T_{\rm C} = 186$\,K. A
magnetic entropy change $\Delta S =
7$\,J\,$\cdot$\,kg$^{-1}$\,$\cdot$\,K$^{-1}$ is observed for a
magnetic field change from 0 to 5\,T. A large value of refrigerant
capacity (RC) is found to be 330\,J/kg for fields ranging from 0 to
5\,T. The large RC, the reversible magnetization around $T_{\rm C}$
and the easy fabrication make the Tb6Co1.67Si3
compound a suitable candidate for magnetic refrigerants in a
corresponding temperature range. 相似文献
19.
Study on incident laser modulation using surface micro-defects on KH<sub>2</sub>PO<sub>4</sub> crystal 下载免费PDF全文
KH2PO4 crystal is a crucial optical component of inertial confinement fusion.Modulation of an incident laser by surface micro-defects will induce the growth of surface damage,which largely restricts the enhancement of the laser induced damage threshold.The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method.The results indicate that after the modulation of surface defects,the light intensity distribution inside the crystal is badly distorted,with the light intensity enhanced symmetrically.The relations between modulation properties and defect geometries(e.g.,width,morphology,and depth of defects) are quite different for different defects.The modulation action is most obvious when the width of surface defects reaches 1.064 μm.For defects with smooth morphology,such as spherical pits,the degree of modulation is the smallest and the light intensity distribution seems relatively uniform.The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value.The critical depth is 1.064 μm for cuboid pits and radial cracks,while for ellipsoidal pits the value depends on both the width and the length of the defects. 相似文献
20.
The optical properties of LaCl3:Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is found that optical transmittance is as high as 80% between 320 nm and 600 nm, and no obvious absorption band is found in this region. Emission intensity and decay time of photoluminescence are quite stable with the change of the temperature between 80 K and 500 K. No thermal quenching is present up to 500 K, and decay time keeps at 17±2 ns. With the increase of the temperature, the whole emission bands and excitation bands present broadening and overlapping, leading to the strengthening of re-absorption of the Ce^3+ emission, which makes the emission spectra have a red shift trend. 相似文献