FLASH-News

 
25-Jul-2023
25-Jul-2023
  • Result defies established models of nanoparticle behaviour

    Photocatalysis, sensors, solar cells: nanoparticles that are excited by light promise a variety of applications, if the processes behind their behaviour can be controlled. One such process is a type of collective electron motions. These movements lead to energy exchange in the nanoparticle that give them their characteristics but that can also be disruptive. However, so far the exact behaviour of those movements was unclear. A research team comprising scientists from the Center for Free-Electron laser Science (CFEL) at DESY, Universität Hamburg, the Max-Planck-Institute for the Structure and Dynamics of Matter, Hamburg, and TU Berlin reports in the journal Nano Letters experimental observations of a molecular movie recorded at DESY’s FLASH free-electron laser that cannot be explained by established models. In response to these findings, the team has provided a new theoretical model that explains their experimentally observed dynamics of the excited gold nanoparticles. The image Illustrates a gold nanoparticle: the researchers found that when activated by a light pulse, the electrons in the particle already shift, far sooner than earlier believed.

    Reference: Time-resolved single-particle X-ray scattering reveals electron-density gradients as coherent plasmonic-nanoparticle-oscillation source; Dominik Hoeing, Robert Salzwedel, Lena Worbs, Yulong Zhuang, Amit K. Samanta, Jannik Lübke, Armando D. Estillore, Karol Dlugolecki, Christopher Passow, Benjamin Erk, Nagitha Ekanayake, Daniel Ramm, Jonathan Correa, Christina C. Papadopoulou, Atia Tul Noor, Florian Schulz, Malte Selig, Andreas Knorr, Kartik Ayyer, Jochen Küpper, Holger Lange; Nano Letters, 2023; DOI:10.1021/acs.nanolett.3c00920
28-Jun-2023
28-Jun-2023
  • Ultrashort Pulses at FLASH

    Ultrashort soft X-ray pulses generated at FLASH made it to the Photonics Cover Story. The presented concept overcomes the coherence time barrier and results in ultrashort pulses in X-ray Free Electron Lasers. As well as a numerical illustration, the results of the first experimental test at the soft X-ray FEL user facility FLASH are presented in Photonics.
    The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free-Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part of an electron bunch is much shorter than the coherence time, one can suppress the radiation in the long main undulator while preserving microbunching within that short lasing slice. Then, a short radiation pulse is produced in a relatively short radiator. A possible suppression method, an excessive reverse undulator taper, is discussed and illustrated numerically. The first experimental tests of this method is performed at the soft X-ray FEL user facility FLASH. The measured pulse duration approaches 1 fs (FWHM) at the wavelength of 5 nm.
    From: Abstracts of the article by E. Schneidmiller Photonics, Volume 10, Issue 6 (June 2023).
    The image shows the Photonics cover story: "This concept overcomes the coherence time barrier and results in ultrashort pulses in X-ray Free Electron Lasers. As well as a numerical illustration, the results of the first experimental test at the soft X-ray FEL user facility FLASH are presented. The measured pulse duration approaches 1 fs (FWHM) with pulse energies of 1.5 µJ at a wavelength of 5 nm. The application of the proposed technique to hard X-ray FELs can open the way to generate extremely short pulses, in the range of a few tens of attoseconds."

    Reference: Schneidmiller, E.; Dreimann, M.; Kuhlmann, M.; Rönsch-Schulenburg, J.; Zacharias, H. Generation of Ultrashort Pulses in XUV and X-ray FELs via an Excessive Reverse Undulator Taper. Photonics 2023, 10, 653. DOI:10.3390/photonics10060653
20-Mar-2023
20-Mar-2023
  • A critical milestone towards FLASH2020+ achieved

    External seeding via Echo-Enabled Harmonic Generation (EEHG) has been established for the first time at FLASH. This is a major step towards FLASH2020+ external seeding, achieved by a major effort of the Xseed team with the support of many FLASH experts. Compared to standard SASE operation, the spectral quality and the longitudinal coherence are drastically improved and will ultimately allow for the next generation of user experiments.

    The image shows a couple of plots related to the experiment. The graphs on the left-hand side illustrates the spectral properties of EEHG and HGHG at 22.1 nm, the 12th harmonic of the seed lasers fundamental of 266 nm. Evident are for example the reduced spectral bandwidth (left bottom) and high spectral reproducibility (left centre). Also the plots on the right-hand side demonstrate that upon variation of the strength of the second (bunching) chicane EEHG has an increased wavelength stability (right centre) and rather broad peak ins spectral intensity (right top). In addition the transverse mode of FLASH2 lasing in SASE mode is shown in the bottom centre.

    EEHG is a seeding technique based on the interaction of the electron beam with two lasers to generate fully coherent and stable FEL pulses at harmonic wavelengths of the 266 nm seed laser (tripled Ti:Sa). In our case, we explored the 9th (29.5 nm), 12th (22.1 nm), 15th (17.7 nm), and 17th (15.6 nm) harmonics. A few selected results taken with the 12th harmonic at 22.1 nm are shown in the image. Here the difference between EEHG and the two operation modes High-Gain Harmonic Generation, overlapping a seed laser with the electron beam in just a single stage, are especially highlighted. While both seeded operation modes provide clean and reproducible spectra in contrast to SASE, the benefit of smallest spectral bandwidth and highest spectral intensity for EEHG is evident.

    A week after the first demonstration the Xseed team was able to timely re-establish EEHG seeding conditions after accelerator maintenance in 4 hours. Among others, this time two electron bunches were distributed to the FLASH1 beamline - mimicking the shortest possible bunch-train. Upon shifting of the seed laser timing the output radiation properties in the two cases could be compared. This is a critical point towards FL2020+, where we plan to seed bunch trains up to 500 bunches at MHz repetition rate.

    In parallel to seeding operation, the FLASH2 beamline was operated in SASE at 30 nm with intensities above 100 uJ and a nice transverse mode. This is another "first" worldwide and a crucial milestone as it demonstrates the feasibility of the future FLASH operation concept.

    We would like to thank everyone involved.
6-Jan-2023
6-Jan-2023
23-Aug-2022
23-Aug-2022
1-Jun-2022
1-Jun-2022
19-May-2022
19-May-2022
03-Mar-2022
03-Mar-2022
2-Mar-2022
2-Mar-2022
21-Jul-2021
21-Jul-2021
22-Apr-2021
22-Apr-2021
FLASH2020+ Kick-Off Meeting 3-Jul-2020
FLASH2020+ Kick-Off Meeting 3-Jul-2020

Impression from the virtual Kick-off meeting of the FLASH2020+ project at DESY on 3 July 2020, including images of the speakers (Credit: DESY).

FLASH2020+ technical design phase started


Making FLASH brighter, faster and more flexible


The technical design phase of the FLASH2020+ project at DESY started with an internal virtual kick-off meeting. Over 270 participants mainly from DESY and the campus in Hamburg joined the project team online on 3 July 2020. Key topics were the upgrade project of the free-electron laser (FEL), scientific goals, the embedding at DESY and the international landscape, the project structure and its timeline over the next five years.

The FLASH2020+ project is based on the long history of FLASH at DESY, from its inception as a test facility for the TESLA project in the mid-90s of the last century to the worldwide first XUV to soft X-ray FEL user facility ten years later. With the FLASH2 project, it is now the first FEL that runs two independent undulator lines in parallel, again about ten years later.

In 2020, yet another ten years later, the project is right in time to make the next step forward with the facility where especially the external seeding and shorter pulses will enable new and unique scientific opportunities. The upgrade will keep FLASH at the forefront of science with FELs for the next decade, as highlighted by Edgar Weckert, director in charge for DESY Photon Science. The importance of the project for the DESY strategy to further advance DESY’s machines and to develop new technologies for future accelerators was stressed by Wim Leemans, the DESY director of the accelerator division. With such a project, DESY contributes also to the technical developments in FEL science and teaching of the next generation of scientists.

The FLASH2020+ project is be led by Enrico Allaria, who presented the project phases, timeline and structure. He is an expert from the FEL “FERMI” in Trieste (Italy) and has just started to work at DESY.

Further information (slides) from the FLASH2020+ kick-off meeting web pages.

application/pdf FLASH2020+: millions for the modernisation towards ultrashort snapshots (904KB)
Press and Public Relations - FLASH2020+
DESY Press and Public Relations - Mai 2020
9-May-2019
9-May-2019
5-Nov-2018
5-Nov-2018
30-Oct-2017
30-Oct-2017
9-Apr-2016
9-Apr-2016
29-Jun-2016
29-Jun-2016
Kai and Albert
Kai and Albert

Kai Siegbahn was awarded the 1981 Nobel Prize in physics for “his contribution to the development of high-resolution electron spectroscopy”.
Albert Einstein received the 1921 Nobel Prize in physics for “his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect”.

14-Jan-2015
14-Jan-2015

10 years of SASE at FLASH

Back in 2005, early in the morning of January 14th, first SASE has been observed at DESY's newly installed VUV free-electron laser. The electron beam has been accelerated to 445 MeV corresponding to a wavelength of 32 nm. In summer 2005, the VUV-FEL turned into a user facility named FLASH.

The image shows the Spectrum of the first SASE signal measured in the early morning of January 14th, 2005.

20-Aug-2014
20-Aug-2014

SASE FEL radiation observed on a Ce:YAG screen of the FLASH2 photon beamline.

24-Feb-2014
24-Feb-2014

Fifth user period started 24-Feb-2014 with its first beam time block

Coming out of a long shutdown to finish up the construction of the new beamline FLASH2, the fifth user period for beamline FLASH1 has started end of February with its first user block. Until April 2015, more than 5000 hours of user experiments are scheduled. Beam time will also be available for accelerator and photon beam line studies as well as for FLASH2 commissioning. FLASH2 saw first beam in March 2014 pushing the beam to the dump for the first time May, 23. Since then, FLASH2 is operated in parallel to FLASH1 whenever possible to finish up the commissioning of beam diagnostics and to refine beam optics. First SASE radiation at 40 nm has been seen on Aug 20, 2014. The next goal is to characterize the SASE radiation, to measure gain length for example for as many other wavelength.

The image shows a schematic layout of FLASH. Not to scale. The second beamline, FLASH2, is being commissioned.

26-Jul-2013
26-Jul-2013

Installation of the new switch yard and extraction beamline to FLASH2 ready to go. The extraction beamline turns to the right through the new opening of the FLASH tunnel towards the FLASH2 beamline hall.

28-Jul-2009
28-Jul-2009