The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on20...The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on2022 July 27.In this paper,we introduce the design and on-ground test results of the LEIA instrument.Using stateof-the-art Micro-Pore Optics(MPO),a wide field of view of 346 square degrees(18.6°×18.6°)of the X-ray imager is realized.An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons,and four large-format complementary metal-oxide semiconductor(CMOS)sensors,each of size 6 cm×6 cm,are used as the focal plane detectors.The instrument has an angular resolution of 4’-8’(in terms of FWHM)for the central focal spot of the point-spread function,and an effective area of 2-3 cm^(2) at 1 keV in essentially all the directions within the field of view.The detection passband is 0.5-4 keV in soft X-rays and the sensitivity is2-3×10^(-11) erg s^(-1) cm^(-2)(about 1 milliCrab)with a 1000 s observation.The total weight of LEIA is 56 kg and the power is 85 W.The satellite,with a design lifetime of 2 yr,operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes.LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation,and by optimizing the working setups of the instrumental parameters.In addition,LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band,albeit with limited useful observing time available.展开更多
Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack grow...Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack growth (FCG) rate and crack path deviation (CPD). The base metal served in a turbine disk of aerospace engine was selected to fabricate bead-on-plate weldments by using electron beam welding. Some wedge-type opening loading specimens, notched in three different zone of weld metal, HAZ and base metal, were employed and performed fatigue crack growth tests at 650℃. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, which means that the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strength zone.展开更多
The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrolog...The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrology systems.Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs.Here,we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL.Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold.These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold,they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time,where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents.A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution,simultaneously,allows us to map the coherently induced trajectory of the Bloch vector.The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications,ranging from efficient intracavity frequency conversion,mode proliferation to passive mode locking.展开更多
基金supported by the Einstein Probe project,a mission in the Strategic Priority Program on Space Science of CAS(grant Nos.XDA15310000,XDA15052100)in part been supported by the European Union’s Horizon 2020 Program under the AHEAD2020 project(grant No.871158).
文摘The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on2022 July 27.In this paper,we introduce the design and on-ground test results of the LEIA instrument.Using stateof-the-art Micro-Pore Optics(MPO),a wide field of view of 346 square degrees(18.6°×18.6°)of the X-ray imager is realized.An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons,and four large-format complementary metal-oxide semiconductor(CMOS)sensors,each of size 6 cm×6 cm,are used as the focal plane detectors.The instrument has an angular resolution of 4’-8’(in terms of FWHM)for the central focal spot of the point-spread function,and an effective area of 2-3 cm^(2) at 1 keV in essentially all the directions within the field of view.The detection passband is 0.5-4 keV in soft X-rays and the sensitivity is2-3×10^(-11) erg s^(-1) cm^(-2)(about 1 milliCrab)with a 1000 s observation.The total weight of LEIA is 56 kg and the power is 85 W.The satellite,with a design lifetime of 2 yr,operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes.LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation,and by optimizing the working setups of the instrumental parameters.In addition,LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band,albeit with limited useful observing time available.
基金National Defense Key Lab for High Energy Density Beam Technology in China for the financial support.
文摘Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack growth (FCG) rate and crack path deviation (CPD). The base metal served in a turbine disk of aerospace engine was selected to fabricate bead-on-plate weldments by using electron beam welding. Some wedge-type opening loading specimens, notched in three different zone of weld metal, HAZ and base metal, were employed and performed fatigue crack growth tests at 650℃. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, which means that the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strength zone.
基金We acknowledge funding from the European Union under the Horizon 2020 research and innovation programs FET-Open grant ULTRAQCL 665158the French National Research Agency(ANR-18-CE24-0013-02-“TERASEL”)+1 种基金the Swedish Research Council(project 2017-04287)the EPSRC(UK)program grant“HyperTerahertz”(EP/P021859/1).
文摘The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrology systems.Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs.Here,we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL.Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold.These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold,they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time,where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents.A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution,simultaneously,allows us to map the coherently induced trajectory of the Bloch vector.The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications,ranging from efficient intracavity frequency conversion,mode proliferation to passive mode locking.
