Making spectral shape measurements in inverse Compton scattering a tool for advanced diagnostic applications

Abstract

Interaction of relativistic electron beams with high power lasers can both serve as a secondary light source and as a novel diagnostic tool for various beam parameters. For both applications, it is important to understand the dynamics of the inverse Compton scattering mechanism and the dependence of the scattered light’s spectral properties on the interacting laser and electron beam parameters. Measurements are easily misinterpreted due to the complex interplay of the interaction parameters. Here we report the potential of inverse Compton scattering as an advanced diagnostic tool by investigating two of the most influential interaction parameters, namely the laser intensity and the electron beam emittance. Established scaling laws for the spectral bandwidth and redshift of the mean scattered photon energy are refined. This allows for a quantitatively well matching prediction of the spectral shape. Driving the interaction to a nonlinear regime, we spectrally resolve the rise of higher harmonic radiation with increasing laser intensity. Unprecedented agreement with 3D radiation simulations is found, showing the good control and characterization of the interaction. The findings advance the interpretation of inverse Compton scattering measurements into a diagnostic tool for electron beams from laser plasma acceleration.

Design study for a compact laser-driven source for medical x-ray fluorescence imaging

“…On the one hand, more photons are emitted into higher harmonics (nE γ ), multiples of the required XFI photon energy. On the other hand, due to the pulsed nature of the laser and the longitudinal and transverse intensity profile, broadening of the x-ray spectrum increases [66,71,75,[81][82][83][84][85][86] as can be seen in nonlinear TS experiments [24,34,[39][40][41]. In a hypothetical laser of constant field amplitude, all electrons would experience the same amplitude during the interaction and thus emit the same photon energy, according to Eq.…”

“…The Thomson process has been extensively studied [8][9][10]13,65,66,[72][73][74][75] and means to maximize the total photon yield N γ and to reduce the bandwidth have been proposed [74,76]. These are evaluated with respect to our special case of a confined radiation cone and compared to simulation results in Sec.…”

“…Depending on its position x, y, z relative to the laser, as well as on the time of interaction t, an electron will experience the laser strength a 0 ðx; y; z; tÞ ≤ a 0 whereâ 0 is defined as the maximum laser strength parameter. The radiated photon energy is then given by [75] E γ ∝ 1 1 þ a 0 ðx; y; z; tÞ 2 =2 : ð7Þ…”

“…Photon production and bandwidth contribution depend on the mean and the width of this distribution, i.e.,ā 0;eff and Δa 0;eff , respectively. As the distribution depends on the laser profile and the overlap of bunch and laser so do μðā 0;eff Þ and ΔE γ ðΔa 0;eff Þ [71,75]. As a consequence, the design requires focal control to optimize laser and electron parameters.…”

Simulation of inverse Compton scattering and its implications on the scattered linewidth

“…It is thus necessary to study how certain interaction parameters of inverse Compton sources-the most important being the properties of the colliding electrons, the incident laser, and the aperture-affect the linewidth of scattered radiation. In the regime where electron recoil is negligible (Thomson regime), numerous studies provide analytical estimates of the dependence of the scattered linewidth (see [11][12][13], and references therein). In the same regime, an innovative scheme of laser chirping has been devised to substantially decrease the linewidth of scattered radiation [14][15][16][17].…”