Electron energy relaxation timeτis one of the key physical parameters for electronic materials.In this study,we develop a new technique to measureτin a semiconductor via monochrome picosecond(ps)terahertz(THz)pump a...Electron energy relaxation timeτis one of the key physical parameters for electronic materials.In this study,we develop a new technique to measureτin a semiconductor via monochrome picosecond(ps)terahertz(THz)pump and probe experiment.The special THz pulse structure of Chinese THz free-electron laser(CTFEL)is utilized to realize such a technique,which can be applied to the investigation into THz dynamics of electronic and optoelectronic materials and devices.We measure the THz dynamical electronic properties of high-mobility n-GaSb wafer at 1.2 THz,1.6 THz,and 2.4 THz at room temperature and in free space.The obtained electron energy relaxation time for n-GaSb is in line with that measured via,e.g.,four-wave mixing techniques.The major advantages of monochrome ps THz pump-probe in the study of electronic and optoelectronic materials are discussed in comparison with other ultrafast optoelectronic techniques.This work is relevant to the application of pulsed THz free-electron lasers and also to the development of advanced ultrafast measurement technique for the investigation of dynamical properties of electronic and optoelectronic materials.展开更多
We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short ...We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short standing-wave buncher between the RF gun and first booster in a conventional S-band photo-injector,electron bunches with a 500 pC charge can be compressed to the sub-picosecond level with very limited input RF power and an unchanged basic layout of the photo-injector.Beam dynamics analysis indicates that fine tuning of the focusing strength of the gun and linac solenoid can well balance additional focusing provided by the standing wave buncher and generate a well-compensated transverse emittance.Thorough bunching dynamics simulations with different operating conditions of the buncher show that a buncher with more cells and a moderate gradient is suitable for simultaneously obtaining a short bunch duration and low emittance.In a typical case of a 9-cell buncher with a 38 MV/m gradient,an ultrashort bunch duration of 0.5 ps(corresponding to a compression ratio of>5)and a low emittance of<1 mm mrad can be readily obtained for a 500 pC electron pulse.This feasible ballistic bunching scheme will facilitate the implementation of an ultrashort pulse mode inverse Compton scattering X-ray source on most existing S-band photo-injectors.展开更多
Hydrothermal reactions of uranyl nitrate and 4,4＇-oxidiphthalic acid（H4L） resulted in the formation of three new uranyl-organic framework materials,namely（NH4）2[（UO2）3（L）2]·5H2O（1）,（NEt4）[（UO2）3（...Hydrothermal reactions of uranyl nitrate and 4,4＇-oxidiphthalic acid（H4L） resulted in the formation of three new uranyl-organic framework materials,namely（NH4）2[（UO2）3（L）2]·5H2O（1）,（NEt4）[（UO2）3（H2O）（L）（HL）]（2） and（UO2）7（H2O）2（phen）4（L）2（HL）2（3）（NEt4 = tetraethylammonium,phen = 1,10-phenanthroline）.These three structures all comprise common uranyl pentagonal bipyramids.In 1,UO7polyhedra are linked by hexadentate ligands to form a 3D framework with 1D channels,in which are located NH4^＋ ions and water molecules.While in 2,the organic ligands adopt pentadentate and hexadentate coordination modes,ligating UO7 units to create a layered structure with channels filled by NEt4^＋ ions.For 3,uranyl square bipyramids are also accommodated together with pentagonal bipyramids,which are linked by tetradentate carboxylate ligands to produce the layered assembly.Phen molecules also coordinate to the uranyl centers to build up the structure.Luminescent studies indicate that 2 and 3 exhibit the characteristic uranyl emission.展开更多
基金the National Natural Science Foundation of China(Grant Nos.U1930116,U1832153,and 11574319)the Fund from the Center of Science and Technology of Hefei Academy of Sciences,China(Grant No.2016FXZY002)。
文摘Electron energy relaxation timeτis one of the key physical parameters for electronic materials.In this study,we develop a new technique to measureτin a semiconductor via monochrome picosecond(ps)terahertz(THz)pump and probe experiment.The special THz pulse structure of Chinese THz free-electron laser(CTFEL)is utilized to realize such a technique,which can be applied to the investigation into THz dynamics of electronic and optoelectronic materials and devices.We measure the THz dynamical electronic properties of high-mobility n-GaSb wafer at 1.2 THz,1.6 THz,and 2.4 THz at room temperature and in free space.The obtained electron energy relaxation time for n-GaSb is in line with that measured via,e.g.,four-wave mixing techniques.The major advantages of monochrome ps THz pump-probe in the study of electronic and optoelectronic materials are discussed in comparison with other ultrafast optoelectronic techniques.This work is relevant to the application of pulsed THz free-electron lasers and also to the development of advanced ultrafast measurement technique for the investigation of dynamical properties of electronic and optoelectronic materials.
基金supported by National Natural Science Foundation of China(NSFC)(Nos.12005211,11905210,11975218 and 11805192).
文摘We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short standing-wave buncher between the RF gun and first booster in a conventional S-band photo-injector,electron bunches with a 500 pC charge can be compressed to the sub-picosecond level with very limited input RF power and an unchanged basic layout of the photo-injector.Beam dynamics analysis indicates that fine tuning of the focusing strength of the gun and linac solenoid can well balance additional focusing provided by the standing wave buncher and generate a well-compensated transverse emittance.Thorough bunching dynamics simulations with different operating conditions of the buncher show that a buncher with more cells and a moderate gradient is suitable for simultaneously obtaining a short bunch duration and low emittance.In a typical case of a 9-cell buncher with a 38 MV/m gradient,an ultrashort bunch duration of 0.5 ps(corresponding to a compression ratio of>5)and a low emittance of<1 mm mrad can be readily obtained for a 500 pC electron pulse.This feasible ballistic bunching scheme will facilitate the implementation of an ultrashort pulse mode inverse Compton scattering X-ray source on most existing S-band photo-injectors.
基金the support of this work by National Natural Science Foundation of China(Nos.21571171,21301168,U1407101)Jilin Province Youth Foundation(No.20130522123JH)
文摘Hydrothermal reactions of uranyl nitrate and 4,4＇-oxidiphthalic acid（H4L） resulted in the formation of three new uranyl-organic framework materials,namely（NH4）2[（UO2）3（L）2]·5H2O（1）,（NEt4）[（UO2）3（H2O）（L）（HL）]（2） and（UO2）7（H2O）2（phen）4（L）2（HL）2（3）（NEt4 = tetraethylammonium,phen = 1,10-phenanthroline）.These three structures all comprise common uranyl pentagonal bipyramids.In 1,UO7polyhedra are linked by hexadentate ligands to form a 3D framework with 1D channels,in which are located NH4^＋ ions and water molecules.While in 2,the organic ligands adopt pentadentate and hexadentate coordination modes,ligating UO7 units to create a layered structure with channels filled by NEt4^＋ ions.For 3,uranyl square bipyramids are also accommodated together with pentagonal bipyramids,which are linked by tetradentate carboxylate ligands to produce the layered assembly.Phen molecules also coordinate to the uranyl centers to build up the structure.Luminescent studies indicate that 2 and 3 exhibit the characteristic uranyl emission.
