Ultrafast high-brightness X-ray pulses have proven invaluable for a broad range of research. Such pulses are typically generated via synchrotron emission from relativistic electron bunches using large-scale facilities. Recently, significantly more compact X-ray sources based on laser-wakefield accelerated (LWFA) electron beams have been demonstrated. In particular, laser-driven betatron sources, where the radiation is generated by transverse oscillations of electrons within the plasma accelerator structure can generate highly-brilliant ultrashort X-ray pulses using a comparably simple setup. Here, we present experimental and simulation data that demonstrate significant enhancement of and control over the parameters of LWFA-driven betatron X-ray emission. With our novel Transverse Oscillating Bubble Enhanced Betatron Radiation (TOBER) scheme, we show a significant increase in the number of generated photons by specifically manipulating the amplitude of the betatron oscillations. We realize this through an orchestrated evolution of the temporal laser pulse shape and the accelerating plasma structure. This leads to controlled off-axis injection of electrons that perform large-amplitude collective transverse betatron oscillations, resulting in increased radiation emission. Our concept holds the promise for a method to optimize the X-ray parameters for specific applications, such as time-resolved investigations with spatial and temporal atomic resolution or advanced high-resolution imaging modalities, and the generation of X-ray beams with even higher peak and average brightness.
A grid of equidistant electron stripes is generated during the collision of two laser pulses under a small angle in underdense plasma. Due to the oblique incidence, transverse standing wave in plasma is observed, in addition to the longitudinal traveling wave of the compound laser field. This standing wave results in the generation of plasma density grating. The ratio of the peak stripe density to background density can reach the value of 20:1. The grating period is determined by the interaction angle. Analytical theory of the compound electric fields is provided for plane waves. The grating formation is then verified via particle-in-cell simulations for short Gaussian laser pulses with typical experimental parameters. In addition, the interference pattern was also observed during experiments with Diocles laser. The results presented here are relevant for many laser-plasma applications, such as Raman scattering, inertial confinement fusion, plasma photonic crystals and laser wakefield acceleration.
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