A paper featuring laser-driven coherent synchrotron emission work carried out on the CLF’s Gemini laser has been chosen as the front cover feature (link opens in a new window) for the latest issue of Physical Review Letters. Collaborators from the UK’s Queen’s University Belfast, Imperial College and Central Laser Facility and Germany’s Max Plank Institute Garching, Ludwig-Maximilians-Universität Munich and Helmholtz-Institut Jena combined experimental and simulation results to produce results that were recently published (link opens in a new window)in the high impact journal Physical Review Letters.
Simulation of attosecond pulse generation (cyan) with electron density plotted against time (vertical) and position (horizontal) during a laser-plasma interaction.
(Credit: M. Yeung et. al., Phys. Rev. Lett. 112, 123902 (2014))
Attosecond science is fast emerging as one of the most exciting and promising fields at the frontier of photonics research. Laser generated attosecond scale (10-18s) pulses offer the possibility to probe the dynamics of electron wavepackets in atomic and molecular systems and may also permit the probing of chemical processes. Recently, it was discovered that periodic trains of such pulses (two pulses per laser cycle) could be generated through coherent synchrotron emission (CSE) from dense electron bunches (PDF - link opens in a new window) with relativistic velocities formed during ultra-high intensity (1020 W/cm2) laser interactions with sub-micron scale foil targets. Attosecond pulses from relativistic mechanisms such as this are desirable over conventional generation techniques because of the higher pulse energies possible which will enable a much wider range of experiments where attosecond pulses can serve as both the pump and the probe for the physical process of interest. A critical step will be to isolate a single attosecond pulse from the pulse trains generated in these interactions.
During a recent experiment on the high power Gemini laser system, the dependence of the efficiency of this transmitted CSE mechanism on the driving laser’s polarization was measured. For circularly polarized light it was observed that the mechanism is effectively switched off. This observation can be exploited by taking a typical ultra-short femtosecond scale laser pulse with several optical cycles and manipulating the polarization such that the pulse is linear for less than one cycle. Numerical simulations add further support to these initial experimental findings by showing that bright isolated attosecond pulses are obtainable from this method using current laser technology, suggesting that pump-probe experiments of attosecond phenomena will be possible in the near future.
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