Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the ...Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the Schottky barrier diode detector in the terahertz frequency band （90–140GHz）. Based on the computed tomography technique, the three-dimensional image of a ceramic sample is reconstructed successfully by stacking the slices at different heights. The imaging results not only indicate the ability of terahertz wave in the non-invasive sensing and non-destructive inspection applications, but also prove the effectiveness and superiority of the uni-traveling-carrier photodiode as a terahertz source in the imaging applications.展开更多
To satisfy the demands for compact,inexpensive terahertz(THz)sources with power of hundreds of watts,a radial sheet beam THz source which does not require an external magnetic field and is driven by a radial pseudospa...To satisfy the demands for compact,inexpensive terahertz(THz)sources with power of hundreds of watts,a radial sheet beam THz source which does not require an external magnetic field and is driven by a radial pseudospark discharge plasma electron gun(PSDP-EGUN)is proposed.Radial design has been used in pseudospark switches,but in this paper the design of a PSDP-EGUN to drive a radial THz source is presented for the first time.Being different from the latest reported axial quasi-rectangular sheet beam THz sources driven by an axial PSDP-EGUN,a new desig n consisti ng of a circular plate-shaped sheet beam that is directly gen erated by the radial PSDP-EGUN is reported.As compared to an axial system,the radial configuration may result in a larger beam current and a larger beam-wave interaction area together with a higher potential of THz output power.Theoretical analysis and pailicle-in-cell simulation have been employed in the design of the radial sheet beam THz source.Output powers in the kilowatt range have been observed in the simulation of this 0.22 THz source.Preliminary experimental results of the radial PSDP-EGUN are also presented.展开更多
The terahertz wave is considered to have great values and plentiful applications, such as in material science, analysis of molecular spectra, information and communication technology, biology and medical science, nond...The terahertz wave is considered to have great values and plentiful applications, such as in material science, analysis of molecular spectra, information and communication technology, biology and medical science, nondestructive evaluation, and national security. High-power widely tunable terahertz sources are required in the above practical applications of terahertz technologies. A promising approach for monochromatic terahertz generation is based on second-order nonlinear optical effect, e.g.展开更多
Strong-field terahertz waves not only have high peak power but also possess strong electromagnetic field components.When electrons encounters strong-field terahertz waves,a series of novel changes are induced,which ha...Strong-field terahertz waves not only have high peak power but also possess strong electromagnetic field components.When electrons encounters strong-field terahertz waves,a series of novel changes are induced,which have attracted extensive attention.This review first introduces common optical sources for strong-field terahertz emission,such as photoconductive antennas,optical rectification crystals,and air plasmas.Subsequently,recent applications of strong-field terahertz technology in material state modulation are presented,mainly including strong-field terahertz wave-driven hot carrier motion,coherent phonon control,spintronics,electron acceleration,and biomedicine.展开更多
Free-space strong-field terahertz(THz)pulses,generated via optical rectification of femtosecond lasers in nonlinear crystals,are pivotal in various applications.However,conventional Ti:sapphire lasers struggle to prod...Free-space strong-field terahertz(THz)pulses,generated via optical rectification of femtosecond lasers in nonlinear crystals,are pivotal in various applications.However,conventional Ti:sapphire lasers struggle to produce high-average-power THz sources due to their limited output power.While kilowatt ytterbium lasers are increasingly adopted,their application in THz generation faces challenges:low optical-to-THz conversion efficiency(attributed to long pulse duration and low energy)and crystal damage under high pumping power.Here,we report a high-average-power strong-field THz source using a lithium niobate crystal pumped by a 1030 nm,570 fs,1 mJ,50 kHz ytterbium femtosecond laser with tilted pulse front pumping(TPFP).By systematically optimizing TPFP implementations and comparing grating-and echelon-type configurations,we achieve a THz source with 64.5 mW average power at 42 W,50 kHz pumping,and focused peak electric field of 525 kV/cm at 0.83 mJ,1 kHz operation.Additionally,we observe Zeeman torque signals in cobalt-iron ferromagnetic nanofilms.This high-repetition-rate,high-average-power THz system,combined with its potential capabilities in high signal-to-noise ratio spectroscopy and imaging,promises transformative impacts in quantum matter manipulation,non-destructive testing,and biomedicine.展开更多
Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacita...Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacitance increases quasi-quadratically with the number of electrodes increasing.The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel.For a photomixer composed of 10 electrodes and 9 photoconductive gaps,the finger capacitance increases as the gap width increases at a small electrode width,and follows the reverse trend at a large electrode width.For a constant electrode width,the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed.We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm × 8 μm photomixer commonly used in previous studies.These calculations lead to a better understanding of the finger capacitance affected by the finger parameters,and should lead to terahertz photomixer optimization.展开更多
We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the as...We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.展开更多
Coherent diffraction radiation (CDR), generated by relativistic femtosecond electron bunches passing through an aperture in a metallic foil, is becoming widely used as a high brightness, coherent, polarized, and broad...Coherent diffraction radiation (CDR), generated by relativistic femtosecond electron bunches passing through an aperture in a metallic foil, is becoming widely used as a high brightness, coherent, polarized, and broad- band terahertz radiation source. It is one of the most promising technique for non-destructive beam diagnostics in ac- celerators. In this paper, how to produce CDR is studied by utilizing femtosecond electron bunches at wavelengths equal to or longer than the bunch length with the aperture size at the condition of a≤γλ/(2π), which is provided by Shanghai Deep Ultraviolet-Free Electron Laser (SDUV-FEL) facility. General characteristics of CDR at SDUV-FEL are analyzed and numerically calculated. The results show that the radiance of this radiation within the frequency range from 0.2 up to 5 terahertz greatly exceeds that available from conventional black body radiation or synchrotron radiation.展开更多
电子束注入器是决定自由电子激光太赫兹源(Free Electron Laser for Terahertz,FEL-THz)性能的核心部件,基于射频加速器的注入器能够产生驱动高功率THz辐射所需的高品质电子束。同时,出于商业化和市场化的考虑,注入器还需具备结构紧凑...电子束注入器是决定自由电子激光太赫兹源(Free Electron Laser for Terahertz,FEL-THz)性能的核心部件,基于射频加速器的注入器能够产生驱动高功率THz辐射所需的高品质电子束。同时,出于商业化和市场化的考虑,注入器还需具备结构紧凑的特点。采用独立调谐式结构(Independently Tunable Cavity,ITC)的束流注入器具有平衡高品质、低成本以及紧凑性的优势,在大功率FEL-THz装置小型化方面有广阔的应用前景。然而,随着束线长度的缩短和装置整体规模的压缩,注入器在运行过程中面临着在线调节手段和诊断能力不足等挑战。本文依托华中科技大学与中国科学技术大学共建的一台紧凑型FEL-THz注入器,首先介绍其基于ITC结构的优化思路和设计结果,然后在系统稳定的基础上,重点阐述调试和运行过程中所涉及的束流间接诊断和系统优化措施,并结合束流动力学仿真和在线实验开展了相关方案和研究的验证。仿真和实验结果均表明,通过优化设计并结合间接诊断技术,ITC注入器能够兼顾FEL-THz高功率和小型化的需求,而间接诊断技术的应用也能够弥补调试过程中诊断手段不足的问题,为ITC注入器的进一步推广奠定了基础。展开更多
We present a specific-window method to subtract the interference of water vapor on terahertz frequency-domain spectroscopy（THz-FDS） at ambient temperature and pressure. A continuous-wave spectrometer based on photom...We present a specific-window method to subtract the interference of water vapor on terahertz frequency-domain spectroscopy（THz-FDS） at ambient temperature and pressure. A continuous-wave spectrometer based on photomixing was utilized to obtain THz-FDS of methanol vapor in the range of 50–1200 GHz. The distinctly spaced absorption features in the neighborhood of atmospheric windows of transparency were selected to perform linear fitting versus the calculated absorption cross section and obtain the concentration of methanol. Furthermore, the gradually decreased methanol vapor was quantified to demonstrate the reliability of the method.展开更多
We investigate a novel Smith–Purcell terahertz source. This device is composed of an electron gun, a cylindrical resonator, a metallic grating, and a collector. The characteristics of the Smith–Purcell terahertz sou...We investigate a novel Smith–Purcell terahertz source. This device is composed of an electron gun, a cylindrical resonator, a metallic grating, and a collector. The characteristics of the Smith–Purcell terahertz source are discussed with the help of three-dimensional particle-in-cell simulation. In this device, coherent and high-power Smith–Purcell radiation(SPR) at the terahertz frequency range can be produced for the reasonable parameters of charge energy and grating. Our results indicate that coherent SPR at 506.529 GHz with a power around 1000 W can be obtained for a grating of period l=0.3 mm operating at the beam energy E=50 keV and beam current I=10 A.展开更多
We present the generation of high-repetition-rate strong-field terahertz(THz)pulses from a thin 4-N,N-dimethylamino-4’-N’-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate(DSTMS)organic crystal pumped by an ytterb...We present the generation of high-repetition-rate strong-field terahertz(THz)pulses from a thin 4-N,N-dimethylamino-4’-N’-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate(DSTMS)organic crystal pumped by an ytterbium-doped yttrium aluminum garnet laser.The generated THz pulse energy reaches 932.8 nJ at 1 kHz repetition rate,with a conversion efficiency of 0.19%and a peak electric field of 819 kV/cm.At a repetition rate of 10 kHz,it is able to maintain a peak electric field of 236 kV/cm and an average THz power of 0.77 mW.The high-repetition-rate,strong-field THz source provides a convenient tool for the study of THz matter manipulation and THz spectroscopy.展开更多
基金Supported by the Hundred Talents Program of Chinese Academy of Sciencesthe National Basic Research Program of China under Grant No 2014CB339803+2 种基金the Major National Development Project of Scientific Instrument and Equipment under Grant No2011YQ150021the National Natural Science Foundation of China under Grant Nos 61575214,61574155,61404149 and 61404150the Shanghai Municipal Commission of Science and Technology under Grant Nos 14530711300,15560722000 and 15ZR1447500
文摘Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the Schottky barrier diode detector in the terahertz frequency band （90–140GHz）. Based on the computed tomography technique, the three-dimensional image of a ceramic sample is reconstructed successfully by stacking the slices at different heights. The imaging results not only indicate the ability of terahertz wave in the non-invasive sensing and non-destructive inspection applications, but also prove the effectiveness and superiority of the uni-traveling-carrier photodiode as a terahertz source in the imaging applications.
文摘To satisfy the demands for compact,inexpensive terahertz(THz)sources with power of hundreds of watts,a radial sheet beam THz source which does not require an external magnetic field and is driven by a radial pseudospark discharge plasma electron gun(PSDP-EGUN)is proposed.Radial design has been used in pseudospark switches,but in this paper the design of a PSDP-EGUN to drive a radial THz source is presented for the first time.Being different from the latest reported axial quasi-rectangular sheet beam THz sources driven by an axial PSDP-EGUN,a new desig n consisti ng of a circular plate-shaped sheet beam that is directly gen erated by the radial PSDP-EGUN is reported.As compared to an axial system,the radial configuration may result in a larger beam current and a larger beam-wave interaction area together with a higher potential of THz output power.Theoretical analysis and pailicle-in-cell simulation have been employed in the design of the radial sheet beam THz source.Output powers in the kilowatt range have been observed in the simulation of this 0.22 THz source.Preliminary experimental results of the radial PSDP-EGUN are also presented.
文摘The terahertz wave is considered to have great values and plentiful applications, such as in material science, analysis of molecular spectra, information and communication technology, biology and medical science, nondestructive evaluation, and national security. High-power widely tunable terahertz sources are required in the above practical applications of terahertz technologies. A promising approach for monochromatic terahertz generation is based on second-order nonlinear optical effect, e.g.
基金supported by the National Natural Science Foundation of China(No.12204251)。
文摘Strong-field terahertz waves not only have high peak power but also possess strong electromagnetic field components.When electrons encounters strong-field terahertz waves,a series of novel changes are induced,which have attracted extensive attention.This review first introduces common optical sources for strong-field terahertz emission,such as photoconductive antennas,optical rectification crystals,and air plasmas.Subsequently,recent applications of strong-field terahertz technology in material state modulation are presented,mainly including strong-field terahertz wave-driven hot carrier motion,coherent phonon control,spintronics,electron acceleration,and biomedicine.
基金Scientific Research Innovation Capability Support Project for Young(ZYGXQNJSKYCXNLZCXMI3)National Key Research and Development Program of China(2022YFA1604402)+1 种基金National Natural Science Foundation of China(U23A6002,92250307)Open Project Program of Wuhan National Laboratory for Optoelectronics(2022WNLOKF006)。
文摘Free-space strong-field terahertz(THz)pulses,generated via optical rectification of femtosecond lasers in nonlinear crystals,are pivotal in various applications.However,conventional Ti:sapphire lasers struggle to produce high-average-power THz sources due to their limited output power.While kilowatt ytterbium lasers are increasingly adopted,their application in THz generation faces challenges:low optical-to-THz conversion efficiency(attributed to long pulse duration and low energy)and crystal damage under high pumping power.Here,we report a high-average-power strong-field THz source using a lithium niobate crystal pumped by a 1030 nm,570 fs,1 mJ,50 kHz ytterbium femtosecond laser with tilted pulse front pumping(TPFP).By systematically optimizing TPFP implementations and comparing grating-and echelon-type configurations,we achieve a THz source with 64.5 mW average power at 42 W,50 kHz pumping,and focused peak electric field of 525 kV/cm at 0.83 mJ,1 kHz operation.Additionally,we observe Zeeman torque signals in cobalt-iron ferromagnetic nanofilms.This high-repetition-rate,high-average-power THz system,combined with its potential capabilities in high signal-to-noise ratio spectroscopy and imaging,promises transformative impacts in quantum matter manipulation,non-destructive testing,and biomedicine.
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2011AAxxx2008A)Hundred Talent Program of the Chinese Academy of Sciences (Grant No. J08-029)the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences (Grant No. YYYJ-1123-4)
文摘Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacitance increases quasi-quadratically with the number of electrodes increasing.The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel.For a photomixer composed of 10 electrodes and 9 photoconductive gaps,the finger capacitance increases as the gap width increases at a small electrode width,and follows the reverse trend at a large electrode width.For a constant electrode width,the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed.We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm × 8 μm photomixer commonly used in previous studies.These calculations lead to a better understanding of the finger capacitance affected by the finger parameters,and should lead to terahertz photomixer optimization.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0701000)the National Key Scientific Instrument and Equipment Development of China(Grant No.2018YFF01013001)the National Natural Science Foundation of China(Grant Nos.61701084 and61505022)。
文摘We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.
文摘Coherent diffraction radiation (CDR), generated by relativistic femtosecond electron bunches passing through an aperture in a metallic foil, is becoming widely used as a high brightness, coherent, polarized, and broad- band terahertz radiation source. It is one of the most promising technique for non-destructive beam diagnostics in ac- celerators. In this paper, how to produce CDR is studied by utilizing femtosecond electron bunches at wavelengths equal to or longer than the bunch length with the aperture size at the condition of a≤γλ/(2π), which is provided by Shanghai Deep Ultraviolet-Free Electron Laser (SDUV-FEL) facility. General characteristics of CDR at SDUV-FEL are analyzed and numerically calculated. The results show that the radiance of this radiation within the frequency range from 0.2 up to 5 terahertz greatly exceeds that available from conventional black body radiation or synchrotron radiation.
文摘电子束注入器是决定自由电子激光太赫兹源(Free Electron Laser for Terahertz,FEL-THz)性能的核心部件,基于射频加速器的注入器能够产生驱动高功率THz辐射所需的高品质电子束。同时,出于商业化和市场化的考虑,注入器还需具备结构紧凑的特点。采用独立调谐式结构(Independently Tunable Cavity,ITC)的束流注入器具有平衡高品质、低成本以及紧凑性的优势,在大功率FEL-THz装置小型化方面有广阔的应用前景。然而,随着束线长度的缩短和装置整体规模的压缩,注入器在运行过程中面临着在线调节手段和诊断能力不足等挑战。本文依托华中科技大学与中国科学技术大学共建的一台紧凑型FEL-THz注入器,首先介绍其基于ITC结构的优化思路和设计结果,然后在系统稳定的基础上,重点阐述调试和运行过程中所涉及的束流间接诊断和系统优化措施,并结合束流动力学仿真和在线实验开展了相关方案和研究的验证。仿真和实验结果均表明,通过优化设计并结合间接诊断技术,ITC注入器能够兼顾FEL-THz高功率和小型化的需求,而间接诊断技术的应用也能够弥补调试过程中诊断手段不足的问题,为ITC注入器的进一步推广奠定了基础。
基金supported by the China Postdoctoral Science Foundation(No.2017M610771)
文摘We present a specific-window method to subtract the interference of water vapor on terahertz frequency-domain spectroscopy（THz-FDS） at ambient temperature and pressure. A continuous-wave spectrometer based on photomixing was utilized to obtain THz-FDS of methanol vapor in the range of 50–1200 GHz. The distinctly spaced absorption features in the neighborhood of atmospheric windows of transparency were selected to perform linear fitting versus the calculated absorption cross section and obtain the concentration of methanol. Furthermore, the gradually decreased methanol vapor was quantified to demonstrate the reliability of the method.
基金National Natural Science Foundation of China(NSFC)(11275089,11375081)Natural Science Foundation of Shandong Province(ZR2011FQ001)
文摘We investigate a novel Smith–Purcell terahertz source. This device is composed of an electron gun, a cylindrical resonator, a metallic grating, and a collector. The characteristics of the Smith–Purcell terahertz source are discussed with the help of three-dimensional particle-in-cell simulation. In this device, coherent and high-power Smith–Purcell radiation(SPR) at the terahertz frequency range can be produced for the reasonable parameters of charge energy and grating. Our results indicate that coherent SPR at 506.529 GHz with a power around 1000 W can be obtained for a grating of period l=0.3 mm operating at the beam energy E=50 keV and beam current I=10 A.
基金supported by the National Key Research and Development Program of China(No.2022YFA1604401)the National Natural Science Foundation of China(Nos.12325409,62105346 and 12388102)+2 种基金the CAS Project for Young Scientists in Basic Research(No.YSBR-059)the Basic Research Project of the Shanghai Science and Technology Innovation Action Plan(No.20JC1416000)the Shanghai Pilot Program for Basic Research–Chinese Academy of Sciences,Shanghai Branch。
文摘We present the generation of high-repetition-rate strong-field terahertz(THz)pulses from a thin 4-N,N-dimethylamino-4’-N’-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate(DSTMS)organic crystal pumped by an ytterbium-doped yttrium aluminum garnet laser.The generated THz pulse energy reaches 932.8 nJ at 1 kHz repetition rate,with a conversion efficiency of 0.19%and a peak electric field of 819 kV/cm.At a repetition rate of 10 kHz,it is able to maintain a peak electric field of 236 kV/cm and an average THz power of 0.77 mW.The high-repetition-rate,strong-field THz source provides a convenient tool for the study of THz matter manipulation and THz spectroscopy.
