组织振动信号的提取是剪切波频散超声振动成像技术(SDUV)方法中的重要步骤.目前,SDUV方法中有两种常用的组织振动信号提取算法,正交解调法(QDM)和互功率谱法(CSM),但是未见比较这两种算法提取质量差异的相关研究.因此,构造了不同信噪比(...组织振动信号的提取是剪切波频散超声振动成像技术(SDUV)方法中的重要步骤.目前,SDUV方法中有两种常用的组织振动信号提取算法,正交解调法(QDM)和互功率谱法(CSM),但是未见比较这两种算法提取质量差异的相关研究.因此,构造了不同信噪比(SNRU)的参数化仿真超声回波信号模型,分别使用QDM和CSM从超声回波信号中提取组织振动信号,比较了两种方法的提取效果与计算效率.实验结果表明,当SNRU≥35 d B,两种算法在相同信噪比下提取出的信号所分离出的振动相位结果相近,标准差均小于1°,对于剪切波波速的计算结果没有太大影响.CSM的计算效率低于QDM的计算效率.因此,当SNRU<35 d B,为了减小振动信号初始相位的提取误差,应该使用CSM提取组织的振动信号.当SNRU≥35 d B,应该选择QDM提取组织的振动信号,以减少信号处理时间.本研究的发现有助于提高SDUV方法的检测效率.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
Using the recently proposed echo-enabled harmonic generation （EEHG） free-electron laser （FEL） scheme, it is shown that operating the Shanghai deep ultraviolet FEL （SDUV-FEL） with single-stage to higher harmonics...Using the recently proposed echo-enabled harmonic generation （EEHG） free-electron laser （FEL） scheme, it is shown that operating the Shanghai deep ultraviolet FEL （SDUV-FEL） with single-stage to higher harmonics is very promising, with higher frequency up-conversion effciency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.展开更多
Coherent light with orbital angular momentum(OAM)is of great interest.Recently,OAM light generation by coupling a relativistic electron beam with a Gaussian mode laser pulse at the high harmonics of a helical undulato...Coherent light with orbital angular momentum(OAM)is of great interest.Recently,OAM light generation by coupling a relativistic electron beam with a Gaussian mode laser pulse at the high harmonics of a helical undulator has been demonstrated experimentally.In this paper,the possibility of delivering coherent OAM light at the 3^(rd)harmonic of the Gaussian mode seed laser is discussed for the Shanghai deep ultraviolet freeelectron laser(SDUV-FEL).Considerations are given on the experiment setup,the expected performance and the possible measurement method.展开更多
文摘组织振动信号的提取是剪切波频散超声振动成像技术(SDUV)方法中的重要步骤.目前,SDUV方法中有两种常用的组织振动信号提取算法,正交解调法(QDM)和互功率谱法(CSM),但是未见比较这两种算法提取质量差异的相关研究.因此,构造了不同信噪比(SNRU)的参数化仿真超声回波信号模型,分别使用QDM和CSM从超声回波信号中提取组织振动信号,比较了两种方法的提取效果与计算效率.实验结果表明,当SNRU≥35 d B,两种算法在相同信噪比下提取出的信号所分离出的振动相位结果相近,标准差均小于1°,对于剪切波波速的计算结果没有太大影响.CSM的计算效率低于QDM的计算效率.因此,当SNRU<35 d B,为了减小振动信号初始相位的提取误差,应该使用CSM提取组织的振动信号.当SNRU≥35 d B,应该选择QDM提取组织的振动信号,以减少信号处理时间.本研究的发现有助于提高SDUV方法的检测效率.
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.
基金Supported by Major State Basic Research Development Program of China (2002CB713600)
文摘Using the recently proposed echo-enabled harmonic generation （EEHG） free-electron laser （FEL） scheme, it is shown that operating the Shanghai deep ultraviolet FEL （SDUV-FEL） with single-stage to higher harmonics is very promising, with higher frequency up-conversion effciency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.
基金Supported by the Major State Basic Research Development Program of China(2011CB808300)the National Natural Science Foundation of China(11175240,11205234 and 11322550)
文摘Coherent light with orbital angular momentum(OAM)is of great interest.Recently,OAM light generation by coupling a relativistic electron beam with a Gaussian mode laser pulse at the high harmonics of a helical undulator has been demonstrated experimentally.In this paper,the possibility of delivering coherent OAM light at the 3^(rd)harmonic of the Gaussian mode seed laser is discussed for the Shanghai deep ultraviolet freeelectron laser(SDUV-FEL).Considerations are given on the experiment setup,the expected performance and the possible measurement method.
