Anomalous Relativistic Emission from Self-Modulated Plasma Mirrors.

Area of Science:

• Plasma Physics
• Laser-Matter Interaction
• Attosecond Science

Background:

• Intense laser pulses interacting with plasma mirrors generate high-order harmonics, producing extreme ultraviolet (XUV) radiation and attosecond pulses.
• Spatiotemporal coherence loss in reflected harmonics was previously considered a limitation.

Purpose of the Study:

• To investigate an unexpected transition in high-harmonic generation from plasma mirrors.
• To explore the phenomenon of directionally anomalous coherent XUV radiation.

Main Methods:

• Analytical calculations.
• Numerical particle-in-cell (PIC) simulations.
• Analysis of laser-driven oscillations of relativistic electron nanobunches.

Main Results:

• Loss of spatiotemporal coherence can lead to a new, highly efficient coherent XUV generation regime.
• Observed anomalous directional propagation of XUV radiation, parallel to the plasma mirror surface.
• Identified laser-driven oscillations of relativistic electron nanobunches, originating from plasma surface instability, as the emission mechanism.

Conclusions:

• Unexpectedly, loss of coherence can enhance efficient coherent XUV generation.
• The discovery of anomalous XUV propagation opens new avenues in attosecond science and coherent radiation sources.
• Plasma surface instabilities play a crucial role in generating novel coherent radiation properties.