Sunday, January 15, 2023

Relativistic Plasma Mirror Driven at a Record-Breaking 1,000 Shots per Second

For the very first time, physicists were successful at driving at a thousand shots per second a so-called plasma mirror in the relativistic reign, i.e. with a laser field so powerful that revolve the plasma electrons back and forth at nearly the speed of light. The achievement was achieved at the LOA (Laboratoire d’Optique Appliquée) in France.

When an enormous laser pulse ionizes the surface of a solid target, it forms plasma so dense that it is impassable to the laser, even if the target was initially transparent. The laser now gets bounce off this “plasma mirror.” In the relativistic reign, the mirror surface no longer just sits calm but is driven to swing so fast that, through a technique called relativistic surface high-harmonic generation (SHHG), it temporally pressed the laser’s electromagnetic field cycles.

This focuses the laser energy further in time and creates plasma mirrors, a promising way for the generation of ever more enormous and shorter laser pulses.

Their utilization and fine control does, however, place very high demands on the driving laser such as pristine spatiotemporal pulse quality and temporal contrast, as well as an enormous peak power of terawatts, i.e. thousands of gigawatts.

This had only been attained in single-shot experiments made with huge lasers that operate at ≤ 10 Hz repetition rate. The team around Stefan Haessler and Rodrigo Lopez-Martens now detect evidence for relativistic SHHG driven at kilohertz repetition rate.

A vital element for this progress is the in-house developed kilohertz repetition rate terawatt laser, giving pulse durations down to <4 femtoseconds and a temporal contrast ratio (between the maximum pulse intensity and 10 picoseconds before) of 1010.

The other is the laser-plasma interaction stand that is altered to the extremely high repetition rate and enables fine control of the interaction order. This is attained notably through a preceding laser pulse which initiates the plasma formation and expansion.

In a next move, the physicists plan to work on refocusing the radiation reflected off the plasma mirror and aim at reaching record-high light intensities for light pulses shorter than a femtosecond.

Reference: ScitechDaily

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