Beam by design: Laser manipulation of electrons in modern accelerators

Abstract

Accelerator-based light sources such as storage rings and free-electron lasers use relativistic electron beams to produce intense radiation over a wide spectral range for fundamental research in physics, chemistry, materials science, biology and medicine. More than a dozen such sources operate worldwide, and new sources are being built to deliver radiation that meets with the ever increasing sophistication and depth of new research. Even so, conventional accelerator techniques often cannot keep pace with new demands and, thus, new approaches continue to emerge. In this article, we review a variety of recently developed and promising techniques that rely on lasers to manipulate and rearrange the electron distribution in order to tailor the properties of the radiation. Basic theories of electron-laser interactions, techniques to create micro-and nano-structures in electron beams, and techniques to produce radiation with customizable waveforms are reviewed. We overview laser-based techniques for the generation of fully coherent x-rays, mode-locked x-ray pulse trains, light with orbital angular momentum, and attosecond or even zeptosecond long coherent pulses in free-electron lasers. Several methods to generate femtosecond pulses in storage rings are also discussed. Additionally, we describe various schemes designed to enhance the performance of light sources through precision beam preparation including beam conditioning, laser heating, emittance exchange, and various laser-based diagnostics. Together these techniques represent a new emerging concept of "beam by design" in modern accelerators, which is the primary focus of this article CONTENTS

Experimental observation of fractional echoes

“…On longer time scales, the interplay b etween the echoes and the quantum revivals [42] shows up both in the exp eriments and in the numerical simulations. The described mechanism of fractional echoes is rather generic, and should b e observed in related systems such as echo-enabled harmonic generation in free-electron lasers (EEHG FEL) in which highly efficient generation of short-wavelength radiation is achieved via laser manipulations over the phase space of relativistic electron b eams [16][17][18][19] .…”

“…Echoes were predict ed to occur in proton storage rings [12 , 13], and were observed in high energy hadron b eam experiments [14,15] . Echo-enabled generation of short-wavelength ra-· diation in free-electron lasers [16][17][18] was demonstrat ed (for a recent review, see [19]) .Recently we reported the exist ence of orienta-· tion/ alignment echoes in an ensemble of free classi-· cal rotors stimulat ed by an external impulsive force [20] . We attributed t he echo formation to the kick-· induced filamentation of the rotational ph ase space, and demonstrated the effect experimentally in a gas of C0 2 molecules excited by a pair of femtosecond laser pulses.…”

“…Echoes were predict ed to occur in proton storage rings [12 , 13], and were observed in high energy hadron b eam experiments [14,15] . Echo-enabled generation of short-wavelength ra-· diation in free-electron lasers [16][17][18] was demonstrat ed (for a recent review, see [19]) .…”

Spin effects probed by Rayleigh X-ray scattering off hydrogenic ions

“…(6). In the present work, we calculate the S-function by adopting the finite basis set method, using B splines and B polynomials as finite basis sets [26][27][28][29][30][31].…”

“…Understanding the effects that spin induces to physical phenomena is of great importance in many branches of applied science and technology like quantum communications, astronomy, chemistry, electronics and so on. Owing to the recent advances in x-ray polarization sensitive detectors [1][2][3], tunable polarization and orbital angular momentum (OAM) free-electron lasers (FELs) [4][5][6][7] as well as synchrotron radiation sources [8], an increasing demand for accurate theoretical prediction on polarization-dependent atomic phenomena is arising. On the other hand, due to the recent progresses in storage rings and trapping techniques the scattering of light by ionic targets is of special interest nowadays since it allows us to obtain information about electron-photon interactions as well as atomic structures in the presence of strong Coulomb field.…”