Speaker
Description
A plasma mirror is formed when an intense laser pulse ionizes a solid target, creating an overdense plasma that reflects light specularly. In the relativistic regime($I \gtrsim 10^{18},\mathrm{W,cm^{-2}}$ at $\lambda = 800,\mathrm{nm}$), plasma mirrors generate high-order harmonics extending into the EUV and soft X-ray range. In the Coherent Synchrotron Emission (CSE) regime, relativistically driven electron nanobunches emit coherent, broadband radiation in attosecond bursts.
Low-order harmonics in the visible/UV can be generated with efficiencies exceeding $20\%$, making relativistic surface high-harmonic generation (RSHG) a promising route to intense, few-cycle pulses across a broad spectral range. At PW-scale facilities, this approach could enable high-power sources in the $200$–$400,\mathrm{nm}$ range and facilitate multi-color waveform synthesis for ultrafast field control. Achieving this requires precise knowledge of the spectral phase, temporal structure, and coherence of the emitted harmonics.
Here, we experimentally characterize the temporal duration and phase of the fundamental using single-shot FROG, and measure the spectral phase and corresponding temporal profiles of the second and third harmonics via spectral interferometry. These measurements are supported by 1D particle-in-cell simulations extending to the fourth harmonic. We observe high mutual coherence and preservation of the driving pulse’s temporal characteristics across harmonic orders.
These results demonstrate that plasma mirrors can generate phase-stable, low-order harmonics suitable for coherent multi-color waveform synthesis, with strong potential for scaling to PW-class ultrafast sources.
This work was supported by the NSF Grants No. PHY 2206711, PHY 2512131, DOE Grant DE-SC0025497, and by the Gordon and Betty Moore Foundation, grant DOI 10.37807/GBMF12255.
| Working group | WG6 |
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