Observation of the Second Harmonic in Thomson Scattering from Relativistic Electrons

Abstract

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.

Angular spectrum characteristics of relativistic inverse compton harmonic X-rays

“…Thus, exact extraction of the 2nd harmonic radiation, with transmission of about 5%, through use of K-edge filtering is verified to be applicable, and this method may be used to deduce the existence of the 2nd harmonic ICS radiation, following Refs. [17,18]. In order to investigate the possible existence of the 3rd harmonic ICS radiation, Al filters with 500, 750 and 1000 μm thickness were used, as shown in Fig.…”

“…The experimental layout of the beam-laser interaction region used a similar geometry as employed in Refs. [17,18]. The pulse length of the electron beam and CO 2 laser are both near to 5 ps FWHM.…”

“…ICS interaction point optics schematic figure-8 motion in linear and nonlinear cases While such laser-induced particle motion has been theoretically investigated during the last few decades [15,16], there have been limited experimental observations of these phenomena. First production of 2nd harmonic ICS photons using a far infrared CO 2 laser was seen in measurements performed at the Brookhaven National Laboratory Accelerator Test Facility (BNL ATF) [17,18]. In this paper, details of the angular and spectral characteristics of the harmonics and the initial generation of 3rd harmonic ICS radiation are reported.…”

“…The spectral characteristics of photons are elucidated by with the use of K-edge filtering [19] along with various attenuation filters in the photon energy of > 10 keV, following the methods reported in Refs. [17,18].…”

Dual color x rays from Thomson or Compton sources

“…Existing Thomson sources [22][23][24][25][26][27][28][29][30][31][32] have already demonstrated to be an important tool for generating tunable quasimonochromatic x=γ rays suitable for applications in many fields such as crystallography, plasma, high energy, matter physics and nuclear photonics and in the advanced biomedical imaging. In fact, experiments on phase contrast imaging [25,27], microtomography [25], K-edge techniques [23,33] on biological and human samples have been successfully performed.…”