Narrow Results

Many of the functionally relevant collective vibrations of proteins and other biopolymers are expected to occur at terahertz frequencies. Precise absorption measurements combined with careful titration of biopolymers in water have allowed us to directly measure the terahertz absorption spectra associated with these motions, despite the strong background absorption of the solvent. We have also explored the circular dichroism spectroscopy of biomolecules over this same frequency range. Since circular dichroism requires the presence of net chirality in a molecule and chirality is present in nearly all biomaterial, it has the potential to capture the background free spectral features in biopolymers. To undertake these studies we have developed a broad band terahertz spectrometer suitable for both direct absorption and circular dichroism measurements of proteins in water between 0.75 – 3.72 THz. Direct terahertz absorption spectra of prototypical proteins bovine serum albumin (BSA) and hen egg white lysozyme have been documented and are described here. We have also successfully demonstrated the magnetic circular dichroism in semiconductors, and placed an upper bound on the terahertz circular dichroism signature of solvated BSA. In the terahertz frequency range, it appears that circular dichroism signatures are exceedingly small and detection remains a challenge.

The physics search potential of the recently proposed FEL ⊗ LHC collider is illustrated in the sample of the collective excitations of the ¹⁵⁴Sm nucleus. In this facility the accelerated fully ionized nuclei will "see" the keV energy FEL photons as a MeV energy laser beam. The main advantages compared to the traditional methods are the tunability, monochromaticity and high polarization of the FEL beam. The advantages result in higher statistics and the possibility to investigate individual levels.

The main parameters of the FEL–RHIC collider are estimated. The physics search potential of this machine is illustrated using excitations of the ²³²Th nucleus as an example. It is shown that, due to the tunability and monochromacity of the FEL beam and high statistics, the proposed collider will play an important role in the field of "traditional" nuclear physics. In addition, spin and parity of nucleus excitations can be easily identified at FEL-nucleus colliders.

Free electron lasers (FELs) are lasers which utilize the phenomenon of stimulated undulator radiation. Contrary to most lasers, the motion of an electron in the FEL may be described by classical mechanics and classical electrodynamics. Therefore, FELs belong to the family of vacuum electronic devices, such as traveling wave tubes or klystrons. In this article, basics of the low-gain FEL physics are discussed and general considerations are clarified through some examples.

The 150 years since Maxwell's formulation of the field equations, Lorentz's formulation of his force law, and Einstein's formulation of special relativity have seen electrodynamics emerge as one of the most fundamental elements of scientific and technical progress in the 20th and 21st centuries. Beginning with the analysis and demonstration of Hertzian waves, these fundamental contributions have launched a series of recurring cycles of discovery and application, in which each new discovery has been exploited to support new applications, which in turn have facilitated additional new discoveries and so on, revolutionizing in the process major elements of our economy with yet more to come through the research now in progress. It is the purpose of this article to relate my recollections of the invention and development of the free electron laser (FEL) within the context of the pervasive influence of the science and technology of electrodynamics in the 20th century.

Energy recovery linacs (ERLs), which can generate an electron beam having a high average current and a small-emittance with the complete manipulation of electron beams in the transverse and the longitudinal phase space, are expected to realize future light sources for various photon energies from terahertz to x- and γ-rays. In this paper, we present an overview of the history, current status, and prospects of ERLs for light sources. Research activities on the critical components of the ERLs, such as electron guns and superconducting cavities, are also described.

As the special machines that can accelerate charged particle beams to high energy by using electromagnetic fields, particle accelerators have been widely applied in scientific research and various areas of society. The development of particle accelerators in China started in the early 1950s. After a brief review of the history of accelerators, this article describes in the following sections: particle colliders, heavy-ion accelerators, high-intensity proton accelerators, accelerator-based light sources, pulsed power accelerators, small scale accelerators, accelerators for applications, accelerator technology development and advanced accelerator concepts. The prospects of particle accelerators in China are also presented.

Many of the functionally relevant collective vibrations of proteins and other biopolymers are expected to occur at terahertz frequencies. Precise absorption measurements combined with careful titration of biopolymers in water have allowed us to directly measure the terahertz absorption spectra associated with these motions, despite the strong background absorption of the solvent. We have also explored the circular dichroism spectroscopy of biomolecules over this same frequency range. Since circular dichroism requires the presence of net chirality in a molecule and chirality is present in nearly all biomaterial, it has the potential to capture the background free spectral features in biopolymers. To undertake these studies we have developed a broad band terahertz spectrometer suitable for both direct absorption and circular dichroism measurements of proteins in water between 0.75 – 3.72 THz. Direct terahertz absorption spectra of prototypical proteins bovine serum albumin (BSA) and hen egg white lysozyme have been documented and are described here. We have also successfully demonstrated the magnetic circular dichroism in semiconductors, and placed an upper bound on the terahertz circular dichroism signature of solvated BSA. In the terahertz frequency range, it appears that circular dichroism signatures are exceedingly small and detection remains a challenge.

As the special machines that can accelerate charged particle beams to high energy by using electromagnetic fields, particle accelerators have been widely applied in scientific research and various areas of society. The development of particle accelerators in China started in the early 1950s. After a brief review of the history of accelerators, this article describes in the following sections: particle colliders, heavy-ion accelerators, high-intensity proton accelerators, accelerator-based light sources, pulsed power accelerators, small scale accelerators, accelerators for applications, accelerator technology development and advanced accelerator concepts. The prospects of particle accelerators in China are also presented.

The 150 years since Maxwell's formulation of the field equations, Lorentz's formulation of his force law, and Einstein's formulation of special relativity have seen electrodynamics emerge as one of the most fundamental elements of scientific and technical progress in the 20th and 21st centuries. Beginning with the analysis and demonstration of Hertzian waves, these fundamental contributions have launched a series of recurring cycles of discovery and application, in which each new discovery has been exploited to support new applications, which in turn have facilitated additional new discoveries and so on, revolutionizing in the process major elements of our economy with yet more to come through the research now in progress. It is the purpose of this article to relate my recollections of the invention and development of the free electron laser (FEL) within the context of the pervasive influence of the science and technology of electrodynamics in the 20th century.

Free electron lasers (FELs) are lasers which utilize the phenomenon of stimulated undulator radiation. Contrary to most lasers, the motion of an electron in the FEL may be described by classical mechanics and classical electrodynamics. Therefore, FELs belong to the family of vacuum electronic devices, such as traveling wave tubes or klystrons. In this article, basics of the low-gain FEL physics are discussed and general considerations are clarified through some examples.

Energy recovery linacs (ERLs), which can generate an electron beam having a high average current and a small emittance with the complete manipulation of electron beams in the transverse and the longitudinal phase space, are expected to realize future light sources for various photon energies from terahertz to x- and γ-rays. In this paper, we present an overview of the history, current status, and prospects of ERLs for light sources. Research activities on the critical components of the ERLs, such as electron guns and superconducting cavities, are also described.