High order harmonics from relativistic electron spikes
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Pirozhkov, Alexander S. Kando, Masaki Esirkepov, Timur Zh. Gallegos, Pablo Ahmed, Hamad Ragozin, Eugene N. Faenov, Anatoly Ya Pikuz, Tatiana A. Kawachi, Tetsuya Sagisaka, Akito Koga, James K. Coury, Mireille Green, James Foster, Peta Brenner, Ceri Dromey, Brendan Symes, Dan R. Mori, Michiaki Kawase, Keigo et al.
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| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/38718 (DOI) | |
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VideoHarmonicComputer animation
Transcript: English(auto-generated)
00:04
This is the Kansai Photon Science Institute, home of J.Karen, a modern ultra-high power laser. Such lasers are fantastic machines. Their peak power exceeds the power of a typical power plant by four to six orders of magnitude. They can generate very sharp pulses consisting of a few light cycles.
00:25
These pulses can be focused down to a micrometer, resulting in tremendous intensities. Such pulses immediately ionize matter, turning it into plasma. Electrons in this plasma move with velocities close to the speed of light.
00:41
This relativistic plasma is home to many remarkable phenomena. Performing experiments with such lasers, we made an exciting discovery. Using the J.Karen laser in Japan and the Astra Gemini laser in the UK, we found that when focused into gas jets, they produced soft X-ray radiation with surprising properties.
01:06
The spectra of this radiation consisted of hundreds of harmonics, with photon energies reaching 360 electron volts, which was the spectrograph limit. The harmonic combs consisted of odd and even orders. The harmonics were generated with both linearly and circularly polarized laser pulses.
01:25
The radiation was very bright. We tried to understand the origin of the observed coherent radiation. Its properties were so unique that they couldn't be explained with previously known mechanisms, such as atomic harmonics, light atom emission, or non-linear Thomson scattering.
01:44
To understand what is going on, we performed particle and cell simulations. Here, the electron density is shown in blue, and the laser intensity with isolines. The laser intensity increases due to relativistic self-focusing. The laser pushes the electrons out, producing an electron-free cavity,
02:03
and generating a wake wave and bow wave. The cusps are the electron density spikes at the joint of the bow wave and the cavity. The coherent X-ray radiation is emitted by the cusps, oscillating under the action of the laser field. The cusp formation is explained with catastrophe theory.
02:23
This is a particle model illustrating it. The top line shows the phase space, where the particle velocity depends on the original location. The particles move, resulting in the phase curve bending and folding. The particle density shown below exhibits spikes at the positions of the phase curve inflection and folds.
02:42
This surface is the combination of the previously shown density profiles. Catastrophe theory states that these singularities, the folds and the cusp, are structurally stable, namely they are robust against perturbations. This is why the harmonic generation occurs in experiments over a wide range of laser and plasma parameters.
03:04
Spectre obtained with a 9 and 120 terawatt lasers reveal a favorable scalability of the harmonic generation with laser power. Our results open the way to compact and coherent X-ray sources based on repetitive lasers and debris-free gas targets.
03:22
This will facilitate X-ray imaging, pan-probe experiments or single-shot other-second science experiments in small arms rather than at large facilities, such as synchrotrons or 3-electron lasers.
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