Recent Experiments at FERMI: The First Fully Coherent, Soft X-Ray Free Electron Laser

Professor Kevin Prince
Elettra Sincrotrone Trieste, Italy and Department of Chemistry and Biotechnology, Swinburne University of Technology

3:30 pm Monday, 1 May 2017, EN101 Lecture Theatre (EN Building), Hawthorn.

Generally, pulsed optical lasers have: high intensity, ultrashort duration, variable polarization, transverse coherence and longitudinal coherence. The majority of short wavelength Free Electron Lasers (FELs) are based on Self Amplified Spontaneous Emission, and possess the first four of these five characteristics, but lack the fifth. The seeded FEL FERMI is the first to produce fully coherent pulses. As well, the longitudinal phase correlation between two colours (first and second harmonics), has been demonstrated and applied to coherently control a photoionization experiment [1]. Neon was ionized at wavelengths of 63.0 and 31.5 nm, and the asymmetry of the 2p photoelectron angular distribution (PAD) was manipulated by adjusting the phase, in a Brumer-Shapiro type experiment [2]. The outgoing 2p electrons, ionized by one (second-harmonic) photon or two (first-harmonic) photons interfere to give an asymmetric PAD whose asymmetry depends on the relative phase of the two photon fields. The relative phase of the two wavelengths was locked and tuned with temporal resolution of ~3 as.
The present results open the door to new coherent control experiments on atoms and molecules in the XUV and soft X-ray region, with ultrahigh time/phase resolution. The flexible design of FERMI has permitted new operating modes of the machine, such as double-pulse operation; production of two coherent, incommensurate colours; and single-colour, phase locked double pulses [3]. The latter open up the way to perform Tannor-Rice or pump-dump type experiments, and results will be shown. Other very recent results will be shown of an apparently unique application of Free Electron Lasers: coherent control of the decay of an excited state ion [4].

[1] K. C. Prince et al. Nature Photon. 10, 176 (2016).
[2] P. Brumer, and M. Shapiro. “Principles of the Quantum Control of Molecular Processes”, Wiley-VCH (2003).
[3] E. Roussel et al., Phys. Rev. Lett. 115, 214801 (2015). D. Gauthier et al., Phys. Rev. Lett. 116, 024801 (2016).
[4] D. Iablonskyi et al., to be published.

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