Research

The H.E.S.S. experiment in Namibia is operated by an international cooperation. The University of Hamburg was one of the few initial German partners since 2000. The large telescopes with up to 600 sqm of mirror surface capture Cherenkov light produced by energetic particles in the atmosphere. The imaging information recorded in an ultra-fast camera is used to determine origin, energy and particle type. This technique has opened the very high energy sky to Astrophysical observations.  

The next generation of ground-based instruments is mainly driven by the development of the Cherenkov telescope array (CTA). We are currently involved in the deployment and commissioning of the first telescopes of the northern site of the CTA observatory on La Palma. In the coming years, these telescopes will be the most sensitive instruments in the energy range above a few 10 GeV up to TeV energies.

This research activity aims at opening up the ultra-high energy gamma-ray regime (energies above 10 TeV and up to PeV), so far only poorly covered. One of the main motivations is the search for Galactic cosmic ray Pevatrons.

HiSCORE is a timing-array concept based on air Cherenkov stations with a wide field of view (30 deg. half opening angle) distributed over a very large area. The first implementation of the HiSCORE concept was realized in the Tunka-valley. After several prototype stages, 28 stations covering an area of 0.25 square-km were installed until 2015. Since this detector stage, the HiSCORE array is part of the TAIGA (Tunka Advanced Instrument for Gamma Ray Astrophysics) experiment.

TAIGA uses a unique approach, combining the timing (HiSCORE) technique with imaging air Cherenkov telescopes (IACTs). A first IACT was installed and commissioned in 2016. Currently (2017), further 30 HiSCORE stations and an additional IACT are being installed in 2017/18. Until 2019, TAIGA will consist of a 1 square-km HiSCORE array and 3 IACTs.

BRASS is a novel experiment for direct, broadband hidden photon and axion/ALP dark matter searches in the 0.02 meV - 5.0 meV (4.8-1200 GHz) range of particle mass. BRASS will employ axion-photon conversion near a permanently magnetized surface, focussing the resulting photon signal onto a set of low-noise heterodyne detectors.

The project is presently concluding the first science runs, offering ample opportunity for research projects in the areas of instrumental design and signal processing.

More details on the experiment are available here.

WISPFI is a table-top, model-independent axion search using a Mach–Zehnder interferometer with a hollow-core photonic crystal fiber (HC-PCF) in the sensing arm. In the full experiment the interferometer is operated at a dark fringe with amplitude locking, while an optical switch alternates two narrow-line lasers at 1535 nm and 1570 nm at 100 kHz. Because only one wavelength satisfies the HC-PCF’s n_eff < 1 resonance for a given axion mass, photon–axion conversion (amplitude loss) occurs only in the corresponding half-cycle. This creates a synchronous amplitude modulation at 100 kHz that is extracted in the dedicated amplitude readout, enabling sensitive detection of $m_a=\omega\sqrt{1-n_\mathrm{eff}^{2}}$ inaccessible to standard dielectric fibers.

The prototype currently under commissioning at Universität Hamburg couples a 2 W, 1550 nm laser into a 1 m-long HC-PCF section embedded in a  ∼ 2 T permanent-magnet array. In this prototype stage the interferometer employs phase locking. A fully automated Python-based DAQ continuously monitors and logs polarization, laser wavelength, beam profile, temperature and humidity, enabling stable long-term unattended integration. The prototype is projected to reach g_aγγ ≳ 1.3 × 10⁻⁹ GeV⁻¹ at m_a ≃ 49 meV over 30 days, making WISPFI the first table-top ALP search capable of probing this unexplored mass region in a DM-independent manner.

WISPFI is designed to be scalable. Pressure tuning of the gas inside the HC-PCF will allow systematic mass scanning between  ∼ 10 –150 meV, while an integrated Fabry–Pérot cavity in the sensing arm will boost the effective optical power and interaction length. This provides a smooth pathway from the table–top prototype towards the full-scale WISPFI implementation capable of probing the QCD axion band and reaching DFSZ sensitivity in a so-far unexplored mass range.

Selected Presentations and Publications

• J.M. Batllori et al., “Searching for weakly interacting sub-eV particles with a fiber interferometer in a strong magnetic field”, Phys. Rev. D 109, 123001 (2024). doi:10.1103/PhysRevD.109.123001.

• J.M. Batllori et al., “WISPFI Experiment: Prototype Development”, in Proc. 19th Patras Workshop on Axions, WIMPs and WISPs (2025). arXiv:2510.01221.

• M. Maroudas, “WISPFI: Towards a Magnet Assisted Fiber Interferometer Search for Axionlike Particles”, 19th Patras Workshop on Axions, WIMPs and WISPs, Granada, 2025. https://agenda.infn.it/event/45898/contributions/271430/

WISPLC (WISP-searches with a LC circuit) is an experiment that searches for dark matter. 

The experiment is currently in its demonstration phase, where key-technologies are being tested and optimised. A more detailed summary of the experiment is given by Zhang et al. (2021)

WINTER

ADAMOS

WispCAV

GravMAGA

This experiment uses a novel broad-band read-out in order to search for Dark Matter at masses below 2 microeV. The results have been published in Nguyen et al. (2019).