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LDM

Low Density Matter at FERMI

The Low Density Matter (LDM) beamline has been built as part of the FERMI free-electron laser (FEL) facility to serve the atomic, molecular and cluster physics community.

The LDM beamline features a modular end-station accommodating a broad range of detectors and systems for producing targets. The combined capabilities of the photon source (high brilliance, short pulse length, variable polarization, coherence), photon transport (variable-focusing optics) and end-station allow the investigation of many targets, such as very dilute systems, matter under extreme irradiation conditions (multiple electronic excitation, multiple ionization, Coulomb explosion, non-linear optics) and dichroism. The split-and-delay line as well as, a synchronized optical laser allows time-resolved experiments with different combinations of femtosecond pulses.

The beamline was commissioned in 2012 and is undergoing rapid development. The LDM beamline is now open to external users .

Research highlights | Publications

Impulsive laser-induced alignment of OCS molecules at FERMI

We have demonstrated laser induced alignment of OCS molecules in the impulsive regime. Revival dynamics were observed for ionic fragments produced after ionization and Coulomb explosion in aligned molecules. M. Di Fraia et al. Physical Chemistry Chemical Physics (2017)

Slow Interatomic Coulombic Decay of Multiply Excited Neon Clusters

Ne clusters (∼5000 atoms) were resonantly excited (2p→3s) by intense free electron laser (FEL) radiation at FERMI. Such multiply excited clusters can decay nonradiatively via energy exchange between at least two neighboring excited atoms. Benefiting from the precise tunability and narrow bandwidth of seeded FEL radiation, specific sites of the Ne clusters were probed. D. Iablonskyi et al. Physical Review Letters, Vol. 117 - 27, pp. 276806 (2016)

Two-photon resonant excitation of interatomic coulombic decay in neon dimers

The recent availability of intense and ultrashort extreme ultraviolet sources opens up the possibility of investigating ultrafast electronic relaxation processes in matter in an unprecedented regime. In this work we report on the observation of two-photon excitation of interatomic Coulombic decay (ICD) in neon dimers using the tunable intense pulses delivered by the free electron laser FERMI. A. Dubrouil et al. Journal of Physics B: Atomic, Molecular and Optical Physics, Vol. 48 - 20, pp. 204005 (2015)

Migration of surface excitations in highly-excited nanosystems probed by intense resonant XUV radiation

Ionization dynamics of resonantly excited helium nanodroplets have been studied by intense XUV light. By doping the nanodroplets with atoms that either attach to the surface or submerge into the center of the droplet, one can study the dynamics of excitation and ionization through the droplet. R. Katzy et al. Journal of Physics B: Atomic, Molecular and Optical Physics, Vol. 48 - 24, pp. 244011 (2015)

Coherent control with a short-wavelength free-electron laser

Here, we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5 nm ionized neon, and we controlled the asymmetry of the photoelectron angular distribution by adjusting the phase, with a temporal resolution of 3 as. K. C. Prince et al. Nature Photonics, Vol. 10 - N, pp. 176-179 (2016)

Time-resolved measurement of interatomic Coulombic decay induced by two-photon double excitation of Ne2

The hitherto unexplored two-photon doubly excited states [Ne*(2p⁻¹3s)]₂ were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. T. Takanashi et al. Physical Review Letters, Vol. 118 - 3, pp. 033202 (2017)

Circular Dichroism in Multiphoton Ionization of Resonantly Excited He Ion

Intense, circularly polarized extreme-ultraviolet and near-infrared (NIR) laser pulses are combined to double ionize atomic helium via the oriented intermediate He+(3p) resonance state. Applying angle-resolved electron spectroscopy, we find a large photon helicity dependence of the spectrum and the angular distribution of the electrons ejected from the resonance by NIR multiphoton absorption. M.Ilchen et al. Physical Review Letters, Vol. 118 - 1, pp. 013002 (2017)

Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters

Intense femtosecond extreme ultraviolet pulses that are well defined in energy and wavelength can efficiently trigger novel collective autoionization mechanisms in nanoscale objects. The process occurs when the photon energy is resonant with excited states of the constituent atoms. This process, here investigated in helium nanodroplets, is expected to be very efficient, and has a general character. Y. Ovcharenko et al., Phys. Rev. Lett (2014).

A modular end-station for atomic, molecular, and cluster science at the Low Density Matter beamline of FERMI

The Low Density Matter end-station at FERMI is used for experiments on atoms, molecules and their aggregates. The charged particles produced by the ionization and fragmentation of the samples by the intense light of FERMI are detected simultaneously and analyzed to yield mass spectra, as well as photoelectron energy and angular distributions. V. Lyamayev et al, J. Phys. B: At. Mol. Opt. Phys (2014).

Determining the polarization state of an EUV FEL beam using atomic circular dichroism

Continuously-variable polarization of FERMI is used here to study dichroic phenomena in photon-matter interactions. The experimental scheme adopted is also an elegant , non-invasive and straightforward method to characterize the polarization properties of XUV FEL beams. T. Mazza et al., Nat. Comm. (2014).

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News

New VMI + TOF setup for LDM

An upgrade of the VMI spectrometer has been designed and built up recently at LDM.
Advantages of the new setup:
•Less sensitive to the misalignment,
•Less sensitive to the stray light,
•Improved ion-TOF collection efficiency.

Scattering detector commissioning at LDM

The LDM scattering detector has been recently commissioned. The image shows the single-cluster scattering pattern from a He droplet of diameter 950 nm, taken with FERMI pulses at a wavelength of 64 nm.

Magnetic bottle commissioning at LDM

A magnetic bottle spectrometer, designed and built by Raimund Feifel and co-workers, has been installed, commissioned, and used for beamtime at LDM. The image shows a test spectrum, with O2 as target gas, taken at 21.2 eV photon energy
[contact: http://www.physics.gu.se/english/about-the-department/staff?languageId=100001&userId=xfeira ]

VMI station at LDM

An experimental station, devoted to experiments on gaseous samples at the Elettra GasPhase beamline and at LDM, was built and commissioned. The station is based on a Velocity Map Imaging detector for angular resolved photoelectron spectroscopy. A thorough description of this photoelectron analyser has been recently published in Nucl. Instr. Meth. B (2011), doi:10.1016/j.nimb.2011.07.020.

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The fourth call for external users is now closed both on FEL-1 and FEL-2.

Last Updated on Wednesday, 19 April 2017 15:36

Elettra-Sincrotrone Trieste S.C.p.A. di interesse nazionale
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