- 标题
- 摘要
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- 实验方案
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Characterization of a double Time-Of-Flight detector system for accurate velocity measurement in a storage ring using laser beams
摘要： The Isochronous Mass Spectrometry (IMS) is a powerful tool for mass measurements of exotic nuclei with half-lives as short as several tens of micro-seconds in storage rings. In order to improve the mass resolving power while preserving the acceptance of the storage ring, the IMS with two Time-Of-Flight (TOF) detectors has been implemented at the storage ring CSRe in Lanzhou, China. Additional velocity information beside the revolution time in the ring can be obtained for each of the stored ions by using the double TOF detector system. In this paper, we introduced a new method of using a 658 nm laser range finder and a short-pulsed ultra-violet laser to directly measure the distance and time delay difference between the two TOF detectors which were installed inside the 10?11 mbar vacuum chambers. The results showed that the distance between the two ultra-thin carbon foils of the two TOF detectors was ranging from 18032.5 mm to 18035.0 mm over a measurable area of 20×20 mm2. Given the measured distance, the time delay difference which comes with signal cable length difference between the two TOF detectors was measured to be ??????????????1?2 = 99(26) ps. The new method has enabled us to use the speed of light in vacuum to calibrate the velocity of stored ions in the ring. The velocity resolution of the current double TOF detector system at CSRe was deduced to be ??(??)∕?? = 4.4 × 10?4 for laser light, mainly limited by the time resolution of the TOF detectors.
关键词： Ultra-high vacuum,Ultra-thin carbon foil,TOF detectors,Velocity measurement,Laser range-finder,ps-pulsed UV laser
更新于2025-11-25 10:30:42
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Velocity-dependent wear behavior of phosphate laser glass
摘要： Using a reciprocating sliding tribometer, the velocity-dependent wear behaviors of phosphate laser (PL) glass were investigated in dry and humid air. The experimental results show that the velocity dependence of wear in PL glass is very sensitive to the presence of water. In dry air, the velocity-dependent wear of PL glass shows fracture-dominated damage behavior. With increasing velocity, the Hertzian cracks increase ?rst and then tend to saturation. Simultaneously, the material-removal volume also increases ?rst and then keeps almost unchanged. However in humid air, the wear mechanism transforms into tribochemistry-controlled wear process, and almost no crack forms on glass surface for various velocities. With increasing velocity, the stress-enhanced hydrolysis becomes weaker and material-removal volume of PL glass decreases sharply. These results may help understand the surface damage and material removal of phosphate laser glass during machining and serving in various conditions.
关键词： Water,Phosphate glass,Velocity,Crack,Tribochemical wear
更新于2025-11-21 11:18:25
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Consideration of the Impact of the Environmental Conditions when Designing Heat-Receiving Systems of the Solar Cylindrical Parabolic Modules
摘要： The aerohydrodynamic and heat exchange characteristics in the cylindrical heat receiver of a solar cylindrical parabolic concentrating module are investigated. The mathematical model is based on the Navier-Stokes equation system for a laminar flow in a channel. The model is implemented using the control volume method. The created computer algorithm allows carrying out parametric studies and revealing the most rational geometric, dynamic, and power parameters of the process. The proposed model describes the general physical outlines of the heat exchange in a cylindrical heat receiver which allows estimating the influence of the environment—wind velocity, ambient temperature, etc.—on it.
关键词： cylindrical heat receiver,rational geometric, dynamic, and power parameters,solar cylindrical parabolic module,wind velocity,Navier-Stokes equation system,ambient temperature,control volume method
更新于2025-09-23 15:23:52
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Robust Optical Flow Estimation Using Tchebichef Moment Invariant Feature
摘要： In this paper, orthogonal moment invariant-based features are used to compute 2D optical flow from sequence of images. The gray level of pixel is described in terms of its local neighborhood using Tchebichef moment invariants rather than its individual intensity value. The description is then normalized in order to make it insensitive to intensity fluctuations due to noise or other perturbations such as varying illumination conditions. The principle of conservation of moment invariance is used to derive overdetermined system of 2D motion constraint equations in local neighborhood of each pixel. The velocity field is then estimated using the least square method. Experimental results are performed on sequential video and thermal image frames under varying environmental conditions. The run time, robustness against noisy and varying illumination conditions and rotation invariance of proposed method are compared with already existing moment and non-moment-based techniques.
关键词： Tchebichef moment,Least square estimation,Moment invariant,Optical flow,Zernike moment,Velocity field
更新于2025-09-23 15:23:52
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Contactless Optical Characterization of Carrier Dynamics in Free-Standing InAs-InAlAs Core-Shell Nanowires on Silicon
摘要： Contactless time-resolved pump-probe and external quantum efficiency measurements were performed on epitaxially grown free-standing wurtzite indium arsenide/indium aluminum arsenide (InAs-InAlAs) core-shell nanowires on Si (111) substrate from 77K to 293K. The first independent investigation of Shockley-Read-Hall, radiative and Auger recombination in InAs-based NWs is presented. Although the Shockley-Read Hall recombination coefficient was found to be at least two orders of magnitude larger than the average experimental values of other reported InAs materials, the Auger recombination coefficient was reported to be ten-fold smaller. The very low Auger and high radiative rates result in an estimated peak internal quantum efficiency of the core-shell nanowires as high as 22% at 77K, making these nanowires of potential interest for high efficiency mid-infrared emitters. A greater than two-fold enhancement in minority carrier lifetime was observed from capping nanowires with a thin InAlAs shell due to passivation of surface defects.
关键词： Auger recombination rate,radiative,Shockley-Read-Hall,Pump-probe spectroscopy,core-shell nanowires,surface/interface recombination velocity,minority carrier lifetime
更新于2025-09-23 15:23:52
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A cryogenic cylindrical ion trap velocity map imaging spectrometer
摘要： A cryogenic cylindrical ion trap velocity map imaging spectrometer has been developed to study photodissociation spectroscopy and dynamics of gaseous molecular ions and ionic complexes. A cylindrical ion trap made of oxygen-free copper is cryogenically cooled down to ～7 K by using a closed cycle helium refrigerator and is coupled to a velocity map imaging (VMI) spectrometer. The cold trap is used to cool down the internal temperature of mass selected ions and to reduce the velocity spread of ions after extraction from the trap. For CO2+ ions, a rotational temperature of ～12 K is estimated from the recorded [1 + 1] two-photon dissociation spectrum, and populations in spin-orbit excited X2Πg,1/2 and vibrationally excited states of CO2+ are found to be non-detectable, indicating an efficient internal cooling of the trapped ions. Based on the time-of-flight peak profile and the image of N3+ ions, the velocity spread of the ions extracted from the trap, both radially and axially, is interpreted as approximately ±25 m/s. An experimental image of fragmented Ar+ from 307 nm photodissociation of Ar2+ shows that, benefiting from the well-confined velocity spread of the cold Ar2+ ions, a VMI resolution of Δv/v ～ 2.2% has been obtained. The current instrument resolution is mainly limited by the residual radial speed spread of the parent ions after extraction from the trap.
关键词： cryogenic ion trap,velocity map imaging,ion cooling,photodissociation,spectroscopy
更新于2025-09-23 15:23:52
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Toward <i>Special-Relativity-on-a-Chip</i> : analogue of Einstein velocity addition using optical add-drop filter (OADF)
摘要： We present an optical analogue of a central concept (not a specific relativistic effect) in Special Relativity (SR) that underlies many relativistic effects. This concept is the Einstein Velocity Addition (EVA) which plays a fundamental role in the development of SR. The photonic circuit analogue is between the EVA, and the complex electric field, through the output signal of the optical add-drop filter (OADF). The OADF is one of the key building blocks for wavelength filtering in photonic integrated circuits (PICs or photonic chip). This analogue strengthens the vision toward a Special-Relativity-on-a-Chip. The analogy is established by equating the two relativistic normalized velocities in EVA with the two transmission coupling coefficients of the two directional couplers in the OADF. Furthermore, the generating angle in the EVA is associated with the single-pass phase shift of the OADF. We analyze its magnitude and directional angle in detail. Lastly, other important consequences are also briefly discussed.
关键词： Special Relativity,Einstein velocity addition,Photonic integrated circuits,microring resonator (MRR),optical add-drop filter (OADF)
更新于2025-09-23 15:23:52
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Evaluation of Low-Temperature Saturation Velocity in β -(Al?Ga???)?O?/Ga?O? Modulation-Doped Field-Effect Transistors
摘要： We report on the high-field transport characteristics and saturation velocity in a modulation-doped β-(AlxGa1?x)2O3/Ga2O3 heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm2/V·s at room temperature to 1520 cm2/V·s at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current–voltage measurements and small-signal radio frequency (RF) measurements. The measured velocity–field profile suggested a saturation velocity above 1.1 × 107 cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency (ft) and maximum oscillation frequency (fmax) showed significant increases from 4.0/11.8 GHz at room temperature to 17.4/40.8 GHz at 50 K for the device with gate length of LG = 0.61 μm. The analysis of the low temperature ft based on device simulations indicated a peak velocity of 1.2 × 107 cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in β-Ga2O3 make it a promising candidate for high-power and high-frequency device applications.
关键词： mobility,β-Ga2O3,modulation-doped field-effect transistor (MODFET),2-D electron gas (2DEG),saturation velocity,high breakdown field
更新于2025-09-23 15:22:29
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Characterization of the Diamond Wire Sawing Process for Monocrystalline Silicon by Raman Spectroscopy and SIREX Polarimetry
摘要： A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, the degree of amorphization of the wafer surface is analyzed, as it may affect the etching performance (texturing) during solar cell manufacture. Raman spectroscopy and Scanning Infrared Stress Explorer (SIREX) measurements are used independently as non-destructive, contactless optical characterization methods to provide stress imaging with high spatial resolution. Raman mappings show that amorphous silicon layers can occur inhomogeneously across the surface of diamond wire-sawn wafers. The Raman and SIREX results reveal a connection between a higher fraction of the amorphous phase, a more inhomogeneous stress distribution and a lower peak maximum of the stress difference on wafers, depending on both the wire wear and the wire velocity. SIREX line scans of the in-plane difference of the principal stress components ?σ taken across the sawing grooves show significant differences in magnitude and periodicity. Furthermore, the results are compared with the microcrack depth from the same investigation areas. The possibility to optimize the diamond wire sawing processes by analyzing the sub-surface stress of the wafers is offered by complementary use of both Raman and SIREX measurements.
关键词： SIREX,wire cutting ability,silicon,microcrack depth,diamond wire,amorphous phase,wire velocity,Raman,stress imaging,stress-induced birefringence
更新于2025-09-23 15:22:29
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Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F<sup>−</sup>
摘要： Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F?), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.
关键词： Chemical physics,Chemistry,gas phase anions,physical chemistry,Issue 137,electronic structure,velocity mapped imaging,photoelectron spectroscopy
更新于2025-09-23 15:22:29