Abstract
Highly energetic electrons are generated at the early phases of the interaction of short-pulse high-intensity lasers with solid targets. These escaping particles are identified as the essential core of picosecond-scale phenomena such as laser-based acceleration, surface manipulation, generation of intense magnetic fields and electromagnetic pulses. Increasing the number of the escaping electrons facilitate the late time processes in all cases. Up to now only indirect evidences of these important forerunners have been recorded, thus no detailed study of the governing mechanisms was possible. Here we report, for the first time, direct time-dependent measurements of energetic electrons ejected from solid targets by the interaction with a short-pulse high-intensity laser. We measured electron bunches up to 7 nanocoulombs charge, picosecond duration and 12 megaelectronvolts energy. Our ’snapshots’ capture their evolution with an unprecedented temporal resolution, demonstrat- ing a significant boost in charge and energy of escaping electrons when increasing the geometrical target curvature. These results pave the way toward significant improvement in laser acceleration of ions using shaped targets allowing the future development of small scale laser-ion accelerators.
Highlights
A direct experimental evidence of these processes requires sub-picosecond measurements of charge density near the surface or alternatively tracing down the escaping electrons
In the following we provide temporally resolved measurements of energetic electrons ejected from solid targets during the interaction with a short-pulse high-intensity laser
The results show that, when using high-power ultra-short laser pulses focused on different target geometries, there is a significant increase in the charge and energy of the escaping electrons when the geometrical target curvature is increased
Summary
A direct experimental evidence of these processes requires sub-picosecond measurements of charge density near the surface or alternatively tracing down the escaping electrons. The results show that, when using high-power ultra-short laser pulses focused on different target geometries (namely planar, wedged and tip shapes), there is a significant increase in the charge and energy of the escaping electrons when the geometrical target curvature is increased It represents a direct evidence of the growth of the electrostatic potential induced near the target surface and an enhancement of the accelerating gradient for the emitted ions. A probe laser (35 fs duration), directly split from the main laser, illuminates the crystal while simultaneously the electron cloud is moving below it Such ultra-short probe laser allows to achieve less than 100 fs as temporal resolution, mainly limited by the implemented electro-optic crystal[24]. More details about the laser system and the implemented EOS diagnostics are presented in sec. [methods] Methods
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