From Event: SPIE Optics + Optoelectronics, 2023
A plasma mirror is an over-dense plasma, created on the surface of a solid target ionized by a high-contrast femtosecond laser. It nonlinearly reflects an ultra-intense laser, resulting in surface high-harmonic generation (SHHG). At relativistic driving intensities, SHHG is a promising candidate for generating intense attosecond pulses, spanning the optical to the EUV spectral ranges.
I will present our recent work on the development of such a source, driven by a waveform-controlled 1.5-cycle (< 4 fs, 780 nm) terawatt laser at 1-kHz repetition rate with extremely high temporal contrast. It allows fine control of the plasma density gradient, maximising the efficiency and spectral extent of relativistic SHHG. At optimal driving laser carrier-envelope-phase (CEP), the SHHG-emission is spectrally continuous and reaches beyond 30eV photon energy. This is the first demonstration of controlled and stable generation of such SHHG continua supporting powerful isolated attosecond pulses. Particle-in-cell simulations predict this emission to be compressed to a sub-femtosecond field transient even without any spectral filtering. We will discuss the experimental challenges related to re-focusing these to high intensity.
Simultaneously and precisely synchronized with the light, MeV-kinetic-energy electron bunches are emitted through vacuum-laser acceleration. Their simultaneously measured spatio-spectral properties also carry clear CEP signatures.
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Stefan Haessler, Jaismeen Kaur, Marie Ouillé, Zhao Cheng, and Rodrigo Lopez-Martens, "Surface high-harmonic generation on a relativistic plasma mirror for generating intense isolated attosecond field transients," Proc. SPIE PC12582, Compact Radiation Sources from EUV to Gamma-rays: Development and Applications, PC125820M (Presented at SPIE Optics + Optoelectronics: April 27, 2023; Published: 8 June 2023); https://doi.org/10.1117/12.2665305.6328682790112.