Generation and Characterization of Betatron X-ray Radiations using High-power Laser Pulses

Abstract

Laser wakefield acceleration （LWFA） provides a compact platform for generating ultrashort, high-energy electron beams and secondary radiation sources. In this work, betatron x-ray radiation generated from a laser wakefield accelerator driven by a 150-TW Ti laser system is experimentally investigated. A 24-fs, 2.7-J laser pulse was focused onto a gas jet target consisting of 97% helium mixed with 3% nitrogen, producing relativistic electrons through ionization injection in the nonlinear wakefield regime. The generated electron beam and betatron radiation were characterized using scintillating screens, imaging plates, and x-ray CCD diagnostics. Electron energies up to 160 MeV were observed. The measured betatron radiation exhibited an elliptical beam profile with full-width at half-maximum （FWHM） divergences of 19 mrad and 11 mrad in the horizontal and vertical directions, respectively. Spectral reconstruction using attenuation filter analysis yielded a critical photon energy of approximately 13 keV, which showed reasonable agreement with analytical estimates based on the measured electron beam and plasma parameters. The x-ray source was further applied to radiographic imaging of mesh structures and biological speci- mens, demonstrating the capability of betatron radiation for high-resolution imaging applications. Analysis of the mesh edge response suggested a source size below 14.5 µm. Using the measured divergence, estimated photon number, reconstructed spectrum, and inferred source size, the peak brilliance of the betatron source was estimated to be on the order of 1021 photons/s/mm2/mrad2/0.1% BW assuming the pulse of 25 fs and source size of 14.5 µm. These results demonstrate generation and characterization of betatron radiation from a compact laser- plasma accelerator system and establish a foundation for future studies on advanced betatron diagnostics, wavefront sensing, and high-resolution ultrafast x-ray imaging.