Artemis highlights

Jesse Petersen using the Artemis materials science chamber

The experimental programme on Artemis focuses on applications of ultrafast laser pulses, and on using XUV pulses generated through high harmonic generation for applications in materials science and gas-phase chemistry.

Angle resolved photoemission spectroscopy using XUV pulses

Clocking the melting transition of charge and lattice order in 1T-TaS2 with ultrafast extreme-ultraviolet angle-resolved photoemission spectroscopy (link opens in a new window)

JC Petersen, S Kaiser, N Dean, A Simoncig, HY Liu, AL Cavalieri, C Cacho, ICE Turcu, E Springate, F Frassetto, L Poletto, SS Dhesi, H Berger and A Cavalleri, Phys Rev Lett, 107 177402 (2011)

These experiments focussed on the layered material tantalum disulphide (TaS2). A short infrared laser pulse induced a phase transition from a Mott insulator to a metal, and then XUV pulses recorded a sequence of snapshots of the electronic structure on a very short timescale. TaS2 exhibits a 'charge density wave' - a regular variation in electron density across the layers of atoms - which makes the atoms settle into star-shaped patterns.

Charge density waves are normally related to interactions between electrons and the crystal structure, while Mott insulators are instead produced by interactions between the electrons themselves. The experiment found that, contrary to expectations, the charge density wave and Mott-insulating states 'melted' simultaneously, suggesting a novel mechanism for charge density waves in this material.

The X-ray movies also revealed a structural relaxation which followed the electronic phase transition, but moving slightly more slowly. It was only possible to observe all these effects because of the improved time resolution and higher photon energy in the Artemis beamline, compared to conventional laser-based tr-ARPES. XUV tr-ARPES looks to be a promising route to disentangling the complex behaviour of exotic materials.

This research was led by Andrea Cavalleri's group at the Max Planck Research Department for Structural Dynamics (link opens in a new window).

Press release.

HHG spectroscopy with long-wavelength pulses

High-order harmonic generation (HHG) from molecules produces spectra that contain information on both the static structure of the molecule and the electron dynamics initiated by interaction with the laser field. Using mid-infrared laser pulses at 1300 nm from Artemis, we are able extend the HHG spectrum to beyond 100 eV at comparatively low intensities, where the molecules are not ionised. This enables us to access the region of the CO2 harmonic spectrum containing information about the structure and dynamics, and to study this region over a wide range of laser intensities. This extra information allowed us to isolate effects arising from sub-laser-cycle electron dynamics triggered by the laser field. This work is an important step towards combining attosecond temporal and angstrom-scale spatial resolution in molecular HHG imaging.

Revealing molecular structure and dynamics through high harmonic generation driven by mid-IR fields (link opens in a new window)

R Torres, T Siegel, L Brugnera, I Procino, Jonathan G Underwood, C Altucci, R Velotta, E Springate, C Froud, ICE Turcu, S Patchkovskii, M Yu Ivanov, O Smirnova, and JP Marangos Phys, Rev A 81 051802(R) (2010)

These experiments were led by the Laser Consortium at Imperial College (link opens in a new window)

Ultrafast biomolecular fragmentation

In research led by the Ultrafast Belfast Research Group (link opens in a new window), we have used femtosecond laser pulses to initiate and control molecular motion on ultrashort timescales. We have imaged the motion of fundamental molecules, and demonstrated control over molecular fragmentation.

Through new techniques using electrostatic ion traps, we are pursuing high-resolution studies of larger polyatomic molecules, with applications for research at the Life-Science interface (link opens in a new window)

Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions (link opens in a new window)

J D Alexander, CR Calvert, RB King, O Kelly, WA Bryan, GRAJ Nemeth, WR Newell, CA Froud, ICE Turcu, E Springate, PA Orr, J Pedregosa-Gutierrez, CW Walter, RA Williams, ID Williams and JB Greenwood, J Phys B 42 154027