Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis

We present a detailed comparison of the measured characteristics of Thomson backscattered x rays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the x rays produced from the interaction are presented and shown to agree well with the simulations.

Figure 1

Schematic of the interaction region for the PLEIADES Thomson x-ray source.

Figure 2

Single shot x-ray beam image detected with the x-ray CCD (a), and $y$ integrated background subtracted intensity profile vs the divergence angle in $x$ for the same image (b).

Figure 3

Optical transition radiation image of the electron beam spot at the interaction (a), and an image from a YAG scintillator taken 0.8 m downstream of the interaction point used to determine the divergence of the electron beam (b).

Figure 4

Reconstructed macroparticle representation of the electron beam divergence (a), and (b) comparison of the measured $x$ integrated electron beam divergence in $y$ (squares) to the distribution function used to construct the macroparticle distribution.

Figure 5

Interaction probability vs x-ray energy for the CCD scintillator (a), and the transmission probability through the laser turning optic (b).

Figure 6

Theoretical intensity profiles determined from the measured laser and electron beam parameters for the case of an $x$ polarized incident laser pulse (a), which corresponds to the measured case (Fig. 2), and a $y$ polarized laser pulse (b).

Figure 7

Measured (dots) and simulated (line) intensity profile along the major (a) and minor (b) axes of the Thomson x-ray beam.

Figure 8

Transmission probability through a 0.125 mm thick Ta foil.

Figure 9

Measured (a) and simulated (b) intensity profiles for the transmission of x rays through a 0.125 mm Ta foil. The measured electron beam energy was 55 MeV, while the energy used in the simulation was 56 MeV.

Figure 10

Measured (a) and simulated (b) intensity profile for x-rays transmitted through a 0.125 mm Ta foil. The measured electron beam energy was 57 MeV, while the energy used in the simulation was 58 MeV.

Figure 11

On axis time-dependent x-ray spectrum of the experimentally produced x-ray beam as determined by the 3D time and frequency-domain code.