At an experiment to drive a free-electron laser with an LPA, researchers characterize the magnetic alignment of one of the undulator segments by using a pulsed wire system.

Electron beams at relativistic energies (tens of MeV and beyond) can generate light in the spectrum’s extreme ultraviolet, X-ray, and gamma-ray regions. This light has numerous scientific and practical applications that can benefit from the compact nature of an LPA.

Our pioneering work involves the development of free-electron lasers at the Hundred-Terawatt Undulator (HTU) beamline. This innovative approach harnesses high-quality electron beams from the LPA, which are then directed into a four-meter-long strong-focusing undulator—an array of strong, permanent magnets of alternating polarity that bend the electron beam back and forth, wringing photons out of it. The potential applications for this compact source of intense, coherent photon beams are vast, including single-shot imaging in biophysics research, material characterization in microelectronics, alternatives to lithography, and femtosecond pump-probe studies in atomic, molecular, and optical (AMO) science.

Thomson scattering is another cutting-edge mechanism we are exploring for producing light at BELLA.  At the Hundred-Terawatt Thomson (HTT) beamline, we employ two high-power laser beams independent of each other but synchronized down to the femtosecond, which are directed into the target chamber. The resulting gamma rays (photons with MeV energy) possess the unique ability to penetrate thick and metallic objects, enabling novel 3D computed tomography (CT) reconstruction with <0.1 mm resolution, as well as single-sided 3D LiDAR with ~1 cm accuracy and material differentiation. These capabilities are useful for security applications and hold promise for a wide range of other practical uses.

Standing over the VISA undulator at the Hundred-Terawatt Undulator (HTU) beamline, two BELLA researchers and the student they are mentoring brainstorm how to apply AI/ML to make a connection between laser stability information and undulator radiation diagnostics.

Another photon production mechanism is the betatron motion of the electrons caused by the magnetic fields within the plasma. The source is intrinsically broad-bandwidth (photon energies from sub-keV to tens of keV), which can be an advantage in some applications, as can the point-source nature of the radiation (which intrinsically ensures micron resolution) and the intense photon flux. Potential applications include single-shot phase-contrast imaging and single-shot X-ray transmission spectroscopy.