Low Density Matter group working in the lab
Photo: Julia Sjöberg

Low Density Matter Physics

Research group
Active research
Project owner
Raimund Feifel

Short description

The Low Density Matter – Structure and Dynamics group of Professor Raimund Feifel is active in several areas of photon science as described below, involving some of the world’s foremost multi-particle coincidence techniques in atomic and molecular physics which are constantly developed within this research environment. The group currently constructs Gothenburg’s first Attosecond Science Facility Attohallen based on a cutting-edge femtosecond OPCPA laser system.

Current group members
Raimund Feifel, Professor of Experimental Atomic and Molecular Physics
Richard Squibb, Research Engineer
Sylvain Maclot, Researcher
Hélène Coudert-Alteirac, Postdoc
Alexander Hinterberger, Postdoc
Veronica Ideböhn, PhD student
Emelie Olsson, PhD student
Måns Wallner, PhD student
Sebastian Andersson, Master student
Honorary Doctor
Prof. John H.D. Eland, Oxford University
Guest Professor
Prof. Majdi Hochlaf, Université Gustave Eiffel, Paris
Guest Researcher
Dr. Andreas Hult Roos, ELI Beam lines, Prague
Visiting Students
Mahmoud Jarraya, University of Tunis El Manar
Amira Ben Krid, University of Tunis El Manar
Laamiri Khouloud, University of Tunis El Manar

Previous group members now work, to name a few examples, as a patent attorney, medical physicist, programmers, urban developer, teacher for mathematics and physics. Many have continued to pursue a career within academia.

Guest Professors and Guest Researchers

Prof. John H.D. Eland, Oxford University, 2007 – 2009, 2010 – 2013, 2015 - 2018

Prof. Sergey Sheinerman, St. Petersburg State Maritime Technical University 2009 – 2010

Dr. Jan Metje, University of Potsdam, 2017

Dr. Olena Kulyk, ELI Beam lines, Prague, 2019

Postdocs and Assistant Professors

Melanie Mucke, Uppsala University, 2011 – 2013

Vitali Zhaunerchyk, Uppsala University and University of Gothenburg, 2013 – 2017

Magdalena Kaminska, 2013

Richard Squibb, Uppsala University and University of Gothenburg, 2013 – 2017, now staff member

Raj Singh, University of Gothenburg, 2014 – 2016

Craig Slater, University of Gothenburg, 2015 – 2016

Doctoral Students (main supervision)

Dimitris Koulentianos, University of Gothenburg, PhD 2019

Andreas Hult Roos, University of Gothenburg, PhD 2019

Jonas Andersson, University of Gothenburg, PhD 2019

Sergey Zagorodskikh, Uppsala University, PhD 2016

Lage Hedin, Uppsala University, PhD 2014

Per Linusson, Stockholm University, PhD 2013

Egil Andersson, Uppsala University, PhD 2011

Master Students, Bachelor Students and Internship Students (main supervision)

David Cole, University of Gothenburg, 2020

Emma Forsmalm, University of Gothenburg, 2020

Malin Forsmalm, University of Gothenburg, 2020

Sven Lundberg, University of Gothenburg, 2020

Ugné Miniotaité, Chalmers University of Technology, 2020

Viktor Axelsson, University of Gothenburg, 2019

Ebba Johansson, University of Gothenburg, 2019

Anthony Teichter, University of Gothenburg, 2019

Pia Kärn, University of Gothenburg, 2017

Måns Wallner, University of Gothenburg, 2016 and 2018, currently PhD student

Fabian Årén, University of Gothenburg, 2016

Jesper Brovall, University of Gothenburg, 2016

Kåre Fridell, University of Gothenburg, 2016

Marcus Dahl, University of Gothenburg, 2015

Nils Carlsson, Chalmers University of Technology, 2015

Armin Azhirnian, Chalmers University of Technology, 2015

Andreas Hult Roos, Uppsala University, 2014

Dimitris Koulentianos, Uppsala University, 2014

Souhila Kaddour, Uppsala University, 2012

Mohamed Elbar, Uppsala University, 2012

Delphine Lebrun, Uppsala University, 2011

Martin Berglund, Uppsala University, 2008

Isak Bakken, Stockholm University, 2008

Per Linusson, Uppsala University, 2008

Aila Gengelbach, Uppsala University, 2007

Benedikt Pfeiffer, Uppsala University, 2007

Meryll Colombet, Stockholm University, 2007

Pernilla Andersson, Uppsala University, 2007

Tommy Karlsson, Uppsala University, 2007

Armieh Fathi Moin, Uppsala University, 2006

The Low Density Matter - Structure and Dynamics group has a longstanding tradition of inter-institutional collaboration and thus maintains an extensive network of at a national and international level. Below is an inexhaustive list of the groups and individuals with whom we directly have collaborated during the last few years, many of which are ongoing.


Lund University

  • Anne L’Huillier’s group
  • Johan Mauritsson’s group
  • Mathieu Gisselbrecht’s group
  • Marcus Dahlström’s group

Stockholm University

  • Eva Lindroth’s group

KTH Royal Institute of Technology

  • Hans Ågren’s group

Lund University

  • Leif Karlsson
  • Maria-Novella Piancastelli


University of Oulu

  • Marko Huttula’s group

United Kingdom

University of Oxford

  • John H.D. Eland

University of Southampton

  • John Dyke

Imperial College London

  • Jon Marangos’ group, Imperial College London
  • Leszek Frasinski, Imperial College London
  • Vitali Averbukh’s group, Imperial College London


ELI Beams, Prague

  • Premysl Kolorenc
  • Jakob Andreasson
  • Maria Krikunova
  • Andreas Hult Roos


Universität Potsdam

  • Markus Guehr’s group

Uni Freiburg

  • Frank Stienkemeier’s group
  • Guiseppe Sansone’s group

Max Planck Institute for the Physics of Complex Systems

  • Jan-Michael Rost

Friedrich-Schiller-Universität Jena

  • Stephan Fritzsche’s group

Technische Universität Chemnitz

  • Dieter Gerlich


Elettra-Sincrotrone Trieste

  • Carlo Callegari
  • Kevin Prince
  • Michele Di Fraia
  • Oksana Plekan

Sapienza Università di Roma

  • Stefano Stranges

Italian National Research Council

  • Vincenzo Caravetta


Sorbonne Université

  • Marc Simon
  • Pascal Lablanquie
  • Francis Penent
  • Stephané Carniato

Université Gustave-Eiffel

  • Majdi Hochlaf

United States of America

University of Connecticut

  • Nora Berrah

Kansas State University

  • Daniel Rolles

Brown University, Rhode Island

  • Lai-Sheng Wang


Rijksuniversiteit Groningen

  • Thomas Schlathölter


Universidad Autónoma de Madrid

  • Antonio Picon
Forskning i Low Density Matter lab
Photo: Julia Sjöberg

Our group performs experimental work at a number of different locations within the University of Gothenburg's Department of Physics, and beyond. Below you can read more about our two Gothenburg based laboratories, and a selection of the facilities we use both in Sweden and abroad.

Soliden laboratory: static high-resolution spectroscopy

  • Magnetic bottle electron spectrometer
  • Electron-ion correlation techniques


Attohallen will be Gothenburg's first attosecond science facility. It will serve to provide flexible and powerful femtosecond and attosecond light sources offering experimental capabilities at high temporal and energy resolution.

There are three core pillars that will form the foundation of this facility:

  • A state of the art OPCPA laser system with multiple outputs, capable of delivering femtosecond pulses with 100-10000 uJ of energy, which will drive a number of new coherent, attosecond duration XUV sources
  • A high resolution, 5 meter long magnetic bottle electron spectrometer and flexible XUV-IR interaction chamber.
  • A new pulsed negative ion source capable of trapping, cooling and delivering bunches of negative ions into the interaction region.

Novel sample delivery systems are currently developed by our group which are foreseen to be available at Attohallen, and we welcome external roll-on instrumentation to be connected to open user ports.

OPCPA laser system

The facility will receive delivery by Q1 of a state-of-the-art laser system built by Light Conversion based on Optical Parametric Chirped Pulsed Amplification (OPCPA) technology, which is capable of delivering broad bandwidth, high energy pulses with few femtosecond duration with high wavelength tunability. The complete system will be formed from several component lasers, whose outputs can also be used individually by users.

  • Seed Laser - Pharos PH2-SP-20W-2mJ. A Ytterbium fibre laser delivers 2 mJ pulses of 300 fs duration at a rate of 10 kHz.
  • High repetition rate OPCPA stage - ORPHEUS-OPCPA-HE. Here the input of the PHAROS is converted to broadband pulses with < 9 fs duration, and 120 uJ of energy at a rate of 10 kHz.
  • High energy OPCPA stage - OPCPA-HE-100. 1% of the pulses from the previous OPCPA stage are selected and amplified by 400 x to create 9 fs pulses with 50 mJ of energy, at 100 Hz.

Each of these outputs will have unique science capabilities, and will eventually be used to generate XUV sources at 100 Hz and 10 kHz repetition rates.

External facilities

The group uses at an international level multiple user facilities as external light sources in our work, comprising collaborations with other universities and research institutes. Here is an (incomplete) list of facilities which we frequently use and/or contribute to:


BESSY II is a third generation synchrotron radiation storage ring operated by the Helmholtz-Zentrum Berlin, Germany ( At this facility, we carry out one to several weeks of beam time per annum.


SOLEIL is another third generation synchrotron radiation storage ring located at the outskirts of Paris ( and is used by us primarily for complementary experiments often in close collaboration with our colleagues from France and elsewhere.


The Linac Coherent Light Source (LCLS), operated by SLAC at Stanford, USA (, became the world's first X-ray free electron laser. Early on, we got involved in a series of atomic and molecular science experiments, where our group demonstrated the innovative multi-particle correlation method called partial covariance mapping for which we had developed a dedicated magnetic bottle instrument. LCLS is currently upgraded to LCLS-II and we are again contributing to the early user experiments.


FERMI is the world's first externally seeded free-electron laser located at the Elettra synchrotron radiation facility in Trieste, Italy ( A magnetic bottle electron spectrometer built by our group in Gothenburg forms a key component of the LDM end station, and is frequently used in a large number of greatly successful experiments which we support.

Lund Laser Center

The Lund Laser Center (LLC) offers world-leading attosecond science capabilities ( We contribute to this environment with one of our magnetic bottle multi-electron-ion spectrometers which is frequently used for cutting-edge experiments utilizing tailored high-order harmonic generation XUV radiation.

ELI Beamlines

ELI Beamlines (, located at the outskirts of Prague, is part of the Extreme Light Infrastructure (ELI) pan-European project providing the world's most intense table top lasers. With ultra-high power (10 PW) and concentrated intensities of up to 1024 W/cm2, it offers users truly unique sources of radiation, enabling pioneering research in fundamental and applied sciences. We currently assist ELI Beamlines in constructing a dedicated multi-electron-ion coincidence instrument based on a magnetic bottle which we look very much forward in using at their facility.

The Low Density Matter – Structure and Dynamics group utilises a variety of technologies to achieve its scientific goals, including versatile electron and ion spectrometers, a variety of pulsed infrared, extreme ultraviolet and X-ray light sources, and a diverse set of sample delivery systems and data processing and analysis routines.

Below you can find a brief summary of the technologies we use and how they are utilised within our research.

Magnetic bottle multi-particle spectrometer

The core technology that drives our scientific investigations is the Magnetic bottle electron spectrometer (MBES). This spectrometer uses a combination of a strong and weak magnetic field to efficiently collect all electrons emitted by a photoionized sample and direct them to a detector placed at the end of a long flight-tube. Since the flight times of the electrons will depend on their kinetic energy, we can directly measure the energies of these electrons by accurately measuring the time difference between the arrival of the photons and the time the electrons are detected.

The MBES, which was realized by our honorary doctor, Prof. John H.D. Eland from Oxford University, to be ideally suited for multi-particle correlation studies due to its versatility, high collection efficiency, and good energy resolution. While well established, our current research activities demand constant refinement and customisation for the unique experimental facilities and sample environments we use. The Low Density Matter group operates four individual spectrometers of this type.

Electron-ion correlation techniques

Any of our four instruments can be used to study simultaneously not only the correlations of multiple electrons, but also of the created ions. This can be done in three different ways; either by using one and the same detector for both the electrons and the ions, or by extracting the ions in opposite direction to the electrons or by projecting the ions sidewise onto a positive sensitive detection system.

Radiation sources

The group uses a variety of radiation sources to initiate the ejection electrons from the samples we are studying. The requirements of these sources are that they produce pulses of light which are of short duration (ns duration or shorter) and preferably of a high repetition rate.

Pulsed helium lamps

By applying a high voltage pulse across a capillary filled with helium gas, the helium will be electronically excited, before decaying by emitting a photon at a number of characteristic wavelengths in the ultraviolet region. By selecting one of these wavelengths with a grating, it is possible to obtain an extremely narrowband source of UV radiation, with pulse durations of only a few ns.

We operate multiple lamps that operate on this principle, that can deliver photons up to 48 eV at repetition rates between 1-5 kHz, and these serve as the primary light source for our high resolution static measurements of multiple ionization processes.

Laser driven sources

Modern, solid state laser systems give us access to high intensity (> 50 mJ) and ultrashort (> 10 fs) pulses of infra-red radiation. The extremely short duration of these lasers allows the study of the chemical dynamics of systems with high temporal precision, and the extreme intensities that can be achieved allow the study of nonlinear, many-photon photoelectric processes.

Femtosecond infra-red laser sources also offer the unique possibility to generate XUV pulses of sub-femtosecond duration suing the process of high harmonic generation (HHG). In the HHG process, a ultrashort IR pulse is focused into a jet of noble gas atoms. The strength of the laser field is sufficient to tunnel ionise the atoms, and the now free electrons are accelerated by the laser field before being driven back into the atom. When the electron recombines, pulses of XUV radiation are emitted. The technique of HHG has allowed researchers to explore the electron dynamics with unprecedented precision.

Our group will soon be commissioning a brand-new cutting-edge OPCPA femtosecond laser system which forms the heart of our upcoming high-order harmonic generation facility Attohallen. Additionally, we frequently contribute to attosecond time resolved experiments at the Lund Laser Center.

Storage ring Synchrotrons

Storage ring synchrotrons (SRSs) are national scale facilities.

In order to accommodate the comparatively high repetition rate of synchrotron radiation facilities (MHz) to the needs of our time-of-flight technique (kHz), we develop mechanical, high-speed chopper systems, which are synchronized to the radio frequency of the storage ring.

We regularly perform experiments at state-of-the-art synchrotron radiation facilities such as BESSY-II in Berlin and SOLEIL in Paris, and plan to use MAX-IV in Lund in the not-too-distant future.

Free-electron lasers

XUV and X-ray free electron lasers are some of the most cutting edge light sources available, using relativistic electron accelerators to generate femtosecond or even attosecond duration pulses in the XUV and soft/hard X-ray regimes with unprecedented brightness.

We have performed experiments at the LCLS in Stanford and FERMI in Trieste.

Multi-particle correlation methods

Coincidence spectroscopy

Coincidence spectroscopy is a technique whereby the energies and masses of all particles (electrons and ions) produced by a photoionization event are measured simultaneously. By measuring these sets of particles in coincidence, it becomes possible to disentangle and disambiguate the multiple different possible processes and uniquely identify the states that are created or accessed during the photoionization event that would be impossible to distinguish in a simple one-dimensional measurement.

Coincidence measurements require that the rate of particle detection is several orders of magnitude less frequent than the repetition rate of the light source in order to avoid false coincidences, where particles from different ionization events are detected simultaneously. This necessitates long measurement times, which can be in excess of several days!

Covariance mapping

At some facilities, such as free-electron lasers, the light repetition rate is too low to perform a true-coincidence experiment within a reasonable time period. In these case we use a method called covariance mapping. This technique, pioneered by our collaborator L.J. Frasinki (Science 246, 4933, pp. 1029) which instead of directly measuring coincident particles, uses the statistical fluctuations of the shot-to-shot spectra to reconstruct the coincidences.

We successfully demonstrated at the world’s first X-ray Free Electron Laser, the LCLS at Stanford, the innovative technique of partial covariance mapping, which also accounts for the statistical fluctuations of the X-ray pulse intensity, and have since used the method for several successful beamtimes at free-electron laser facilities.

Production of neutral and charged samples

In order to measure the properties of our target samples with our coincidence methods, we need to generate atoms or molecules that exist in the gas-phase. Depending on the stability of the sample we are interested in, this requires a number of different methods to generate and store them.

Neutral targets

Neutral, stable targets can be efficiently studied in the gas-phase by using an effusive needle, or a supersonic jet. Gases and liquids can be used directly. For low vapour pressure liquids or solid samples (like metals or large organic compounds), we use an effusive oven to heat an evaporate the sample.

Some samples can either not be procured commercially or are so short-lived that they can not be stored for long periods. In the case that the sample's lifetime is sufficient to last for the duration of an experiment, our group members can prepare the samples by chemical synthesis using chemistry lab facilities available at either the Department of Physics here in Gothenburg, or local to the facilities where we perform our experiments.

Radicals and transient species

Some species are so reactive that it is impossible to store them without them either decomposing or reacting with the storage vessel itself. In these cases the samples are produced directly on the experimental apparatus.

Reactive intermediates and transient molecules can be produced using a pyrolysis source. A precursor molecule is sent through a capillary heated above the decomposition temperature of the molecule. The molecule undergoes pyrolysis, generating a number of different products that can the be allowed into the spectrometer to be studied.

Radicals, which are species that have an unpaired valence electron, can be produced using a microwave cavity whereby a precursor molecule is split into radicals by using a cavity of microwave radiation.

Our group is actively developing new and refined versions of these types of sources.

Negative ion sources

The latest developments of our techniques aim to extend this type of spectroscopy to negative ion species. For this purpose, we are currently developing a new negative ion source that will be capable of delivering pulses of cooled negative ions.

International outlook

The environment of the group is truly international, both in its composition and the way research is carried out. Complementary to in-house research activities, the group frequently leads and collaborates on experiments carried out at national and international light sources, like the synchrotron radiation facility BESSY-II in Berlin, the Free-Electron Laser facility FERMI in Trieste and the Lund Laser Center.

Many of the group’s experimental research activities are supported by theoretical modelling primarily carried out by collaborating experts, and most recently also by some of the group members.

Photo: Julia Sjöberg

Reserach projects

Multiply ionised reactive intermediates

Reactive intermediates are atoms and molecules which exist only briefly under normal conditions before they undergo further reaction. These species and their ionised forms play a central role in the interstellar medium, the earth’s and other planetary atmospheres, and in plasmas, and are relevant to practical applications such as matrix-assisted laser desorption ionisation mass spectrometry and the fine control of plasma etching processes.

To date, only photoelectron spectra representing their singly-ionised forms are known; the overall aim of this project is to measure the spectra and decay dynamics of doubly and more highly charged ions derived from reactive species, an essentially new field which we just started.

The project capitalises on an exceptional opportunity to combine our experience of multi-electron-ion spectroscopic techniques with established methods for the production of reactive species, and with vacuum ultraviolet and X-radiation provided by state-of-the-art light sources for ionisation." -> "The project capitalises on an exceptional opportunity to combine this technique with established methods for the production of reactive species, which we get advised on by pioneers in the field, and with vacuum ultraviolet and X-radiation provided by state-of-the-art light sources for ionisation.

This project is primarily financed by the Swedish Research Council (VR).

XUV and X-ray ultrafast spectroscopy

The recent advent of Free-Electron Laser sources operating in the XUV and X-ray spectral region, like FLASH in Hamburg, the Linac Coherent Light Source (LCLS) at Stanford, the SCSS and SACLA facilities in Hyogo, and FERMI in Trieste, in parallel to the continuing technical advances in the creation of (sub-) femtosecond radiation pulses with high harmonic generation (HHG) sources have turned the dream of recording molecular movies with femtosecond temporal and atomic scale structural resolution into reality.

Fundamental questions which are at the heart of ultrafast photo-dynamics of molecular and cluster systems, in particular in photoinduced chemical reactions, are:

  • What is the timescale for the reaction?
  • Can we watch the making and breaking of chemical bonds in real time?
  • Is it possible to catch some intermediate species?
  • Is it possible to manipulate and control the system by varying some instrumental parameters?

From a technical point of view, answers to these questions can be obtained by ultrafast time-resolved pump-probe photoelectron-photoion spectroscopy as very recently demonstrated by us and many collaborators with one of our multi-particle correlation spectrometer stations frequently employed by FERMI. In fact, this has just become an exciting new field at the boundaries between atomic, molecular and cluster science, which is expected to have a profound impact on our understanding of chemical reaction mechanisms and chemical reaction dynamics in general.

Moreover, the same instrumentation has been used by several of our collaborators in order to demonstrate novel attosecond timing capabilities of FERMI which are complementary to table-top high-order-harmonic generation sources.

This project received primarily funding from the Swedish Research Council (VR) and the Knut and Alice Wallenberg Foundation, Sweden.

Multiple detachment of negative ions

Negative ions (anions) are quantum systems formed by neutral atoms or molecules capturing one or several additional electrons. Mono-anions may be dipole-bound, with near zero electron affinities, or valence-bound with positive electron affinities of up to a few eV. Dianions, which are particularly interesting to us, exist as polyatomic species only and may even have negative electron affinities as they are stabilized against auto-detachment by repulsive Coulomb barriers.

Because electrons in negative ions feel less Coulomb attraction to the nucleus than those in neutral or positive species, electron correlation plays a more major role in their binding. The overall goal with this project is to characterise the emitted electron distributions and correlation between all the charged particles produced upon multiple detachment of negative ions. This will lead to the discovery of new electronic states of ions and neutrals and to new physics in the charged-particle dynamics of their formation, stability and destruction. In order to execute this goal, we are in the process of setting up a state-of-the-art facility for the production and manipulation of negative ions which will be combined with one of our multi-particle correlation spectrometry stations and our upcoming high power OPCPA laser system.

There is great interest in such experiments for their relevance to intense radiation environments like the Earth’s outer atmosphere and interstellar space. Also, they will test current atomic and molecular structure theories to their limits, far beyond the frequently used independent particle model.

This project is primarily financed by the Olle Engkvist Byggmästare Foundation, Sweden.

Attosecond chronoscopy of electron emission processes

If an atom, molecule or surface absorbs a photon of sufficiently high energy, an electron may be ejected. This ‘photoelectric’ effect marked the foundation of quantum mechanics and has been tacitly regarded as instantaneous until very recently, when newly available attosecond light pulses enabled measuring real delays in the physical process.

The development of such attosecond-precise time measurements offers the opportunity for a revolution in atomic and molecular physics as interpreted by quantum mechanics, where the issue of time as an observable is a longstanding challenge. The overall aim of this project is testing the quantum mechanical description of time-dependent phenomena.

This will be done here in Gothenburg by characterizing both in phase and amplitude electron wave-packets primarily ejected from negative ions to answer fundamental questions, which are guided by time-dependent many-body theory developed by our collaborators. In order to make that happen, we are in the process of setting up, in close collaboration with the Lund Laser Center, a completely new and for Gothenburg the first attosecond science facility called Attohallen which will comprise a cutting-edge high power OPCPA laser system with two output arms feeding two high-order-harmonic generation beam lines, of which one will be optimized for high photon flux and the other for high pulse repetition rate, a state-of-the-art facility for the production and manipulation of negative ions as well as multi-particle correlation spectrometry stations.

In parallel, attosecond time-resolved photoionization experiments on neutral systems led by our collaborators at the Lund Laser Center are carried out where one of our multi-particle correlation spectroscopy station is used.

This project is primarily financed by the Knut and Alice Wallenberg Foundation, Sweden.