Abstract
Compton scattered x-rays can be generated using a configuration consisting of a single ultrashort laser pulse and a shaped gas target. Upon ionization the gas target serves as a plasma mirror that reflects the incident pulse providing a counter-propagating electromagnetic wiggler. While plasma mirrors are often conceived as linear Fresnel reflectors, we demonstrate that for high-intensity, ultrashort laser pulses the reflection results from two distinct nonlinear mechanisms. At lower densities, the reflection arises from the emission of an electromagnetic pulse during the saturation of the absolute Raman instability at the quarter critical surface. At higher densities the reflection of the pulse from the critical surface sets up a density fluctuation that acts as a Bragg-like reflector. These mechanisms, occurring in a non-perturbative regime of laser–plasma interactions, are examined numerically in order to characterize the Compton scattered radiation.
Highlights
Relativistic electrons counterpropagating with respect to a laser pulse undergo rapid oscillatory motion in the pulse’s electromagnetic field
Through simulation, a novel scheme for single pulse Compton backscattering
The schemes relies on the intersection of a hydrodynamically launched shock wave and gas jet flow to form an underdense to near critical density spike [12,13]
Summary
Relativistic electrons counterpropagating with respect to a laser pulse undergo rapid oscillatory motion in the pulse’s electromagnetic field. The bulk of the pulse undergoes a partial Poynting flux reversal from the ionized spike, providing a counterpropagating field This field Compton backscatters from electrons accelerated in the wakefield driven by the incident pulse. Using the full format PIC simulation TurboWAVE [14], we investigate the Poynting flux reversal and resulting Compton spectrum as a function of incident pulse amplitude and plasma spike profile. This includes a discussion of 3D effects. To change the laser pulse’s angle of incidence with respect to the spike, the spike profile was rotated in the x-z plane, while keeping the propagation axis aligned with the z-axis
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