Category: FELBE / TELBE

Ultrafast and tunable

Ultrafast and tunable

Terahertz-to-visible light conversion for future telecommunications

A study carried out by a research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Catalan Institute of Nanoscience and Nanotechnology (ICN2), University of Exeter Centre for Graphene Science, and TU Eindhoven demonstrates that graphene-based materials can be used to efficiently convert high-frequency signals into visible light, and that this mechanism is ultrafast and tunable, as the team presents its findings in Nano Letters (DOI: 10.1021/acs.nanolett.3c00507). These outcomes open the path to exciting applications in near-future information and communication technologies.

The ability to convert signals from one frequency regime to another is key to various technologies, in particular in telecommunications, where, for example, data processed by electronic devices are often transmitted as optical signals through glass fibers. To enable significantly higher data transmission rates future 6G wireless communication systems will need to extend the carrier frequency above 100 gigahertz up to the terahertz range. Terahertz waves are a part of the electromagnetic spectrum that lies between microwaves and infrared light. However, terahertz waves can only be used to transport data wirelessly over very limited distances. “Therefore, a fast and controllable mechanism to convert terahertz waves into visible or infrared light will be required, which can be transported via optical fibers. Imaging and sensing technologies could also benefit from such a mechanism,” says Dr. Igor Ilyakov of the Institute of Radiation Physics at HZDR.

Read more on the HZDR website

Image: A graphene-based material converts incoming terahertz pulses (from above) into visible light in an ultrafast and controllable manner – optimal for data transport in optical fibers.

Credit: B. Schröder/HZDR

Magnetic sandwich mediating between two worlds

Magnetic sandwich mediating between two worlds

Scientists couple terahertz radiation with spin waves

An international research team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has developed a new method for the efficient coupling of terahertz waves with waves of much shorter wavelengths, so-called spin waves. As the experts report in the journal Nature Physics (DOI:  10.1038/s41567-022-01908-1), their experiments, in combination with theoretical models, clarify the fundamental mechanisms of this process previously thought impossible. The results are an important step for the development of novel, energy-saving spin-based technologies for data processing.

“We were able to efficiently excite high-energy spin waves using terahertz light in a sandwich-like material system consisting of two metal films a few nanometers thick, with a ferromagnetic layer sandwiched in between,” says Dr. Sergey Kovalev of the Institute of Radiation Physics at HZDR, where the experiments were conducted. Electrons have an effective spin which behaves like a spinning top. And like a gyroscope, an external perturbation can tilt the spin’s axis of rotation: A gyroscopic motion, called precession, follows suit. In ferromagnetic materials, there is a very strong interaction between the electron spins, and as a result, a precession started locally continues in the form of a spin wave throughout the ferromagnetic material layer. This is interesting because a spin wave – like any wave – can be used as an information carrier.  While each electron spin is in motion, in the ferromagnets considered it remains in its position in the atomic lattice, therefore no current flow is involved. So, unlike in today’s computer chips, there are no heat losses due to currents in spin-based devices.

Read more on the HZDR website

Image: A terahertz light wave (from left) is converted into a spin wave (right) in a sample of thin metallic layers. In a heavy metal layer (left), electrical currents are first excited by the terahertz field. Within an ultrashort time, the spin Hall effect leads to the accumulation of spins with a certain orientation at the interface with a ferromagnetic layer (right). This directed spin current then triggers a coherent, nanomater-wavelength spin wave in the ferromagnetic material.

Credit: HZDR/Juniks

If at first you don’t succeed…….

If at first you don’t succeed…….

For our final Monday Montage, we focus on the benefits of perseverance and our ability as humans to dig deep and remain determined even when things are going wrong. Maximilian Obst, one of the FELBE (HZDR) users, and Michele Manfredda, from FERMI at Elettra, give honest and insightful accounts of their light source experimental experiences. Light sources are complex scientific tools. They are challenging to build, optimise and utilise. But by continuing to overcome obstacles and working as a team, great and unexpected results can appear. Often these results are obtained in the middle of the night or towards the end of a very long shift on the beamline. However, the lucky few who observe them realise they are the first people in the world to have gleaned this knowledge. Perseverance pays off!

The machine is alive!

The machine is alive!

As our #LightSourceSelfies campaign nears completion, we visit Germany and the Radiation Source ELBE, which is the largest and most versatile research instrument of the HZDR. The electron beam of the superconducting linear accelerator delivers different kinds of secondary radiation for various research purposes from materials science up to medicine. Michael Klopf began his light source career in the USA and is now one of ELBE’s Free Electron Laser (FEL) Beamline Scientists. He explains his career path and the highlights of his diverse role. Viewers also get to see where the experiments happen and hear from Maximilian Obst, one of the FELBE users, who gives a fascinating insight into his near-field optics research using SNOM (Scanning Near-field Optical Microscopy). Maximilian explains how FELBE is enabling science that would not be possible with a synchrotron light source.

Power boost thanks to gold lamellae

Power boost thanks to gold lamellae

Research team develops new material system to convert and generate terahertz waves

On the electromagnetic spectrum, terahertz light is located between infrared radiation and microwaves. It holds enormous potential for tomorrow’s technologies: Among other things, it might succeed 5G by enabling extremely fast mobile communications connections and wireless networks. The bottleneck in the transition from gigahertz to terahertz frequencies has been caused by insufficiently efficient sources and converters. A German-Spanish research team with the participation of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now developed a material system to generate terahertz pulses much more effectively than before. It is based on graphene, i.e., a super-thin carbon sheet, coated with a metallic lamellar structure. The research group presented its results in the journal ACS Nano (DOI: 10.1021/acsnano.0c08106).

Some time ago, a team of experts working on the HZDR accelerator ELBE were able to show that graphene can act as a frequency multiplier: When the two-dimensional carbon is irradiated with light pulses in the low terahertz frequency range, these are converted to higher frequencies. Until now, the problem has been that extremely strong input signals, which in turn could only be produced by a full-scale particle accelerator, were required to generate such terahertz pulses efficiently.“This is obviously impractical for future technical applications,” explains the study’s primary author Jan-Christoph Deinert of the Institute of Radiation Physics at HZDR. “So, we looked for a material system that also works with a much less violent input, i.e., with lower field strengths.”

Read more on the HZDR website

Image: Ultra-thin gold lamellae drastically amplify the incoming terahertz pulses (red) in the underlying graphene layer, enabling efficient frequency multiplication.

Credit: HZDR/Werkstatt X

Dynamic, yet inertial – and definitely futuristic

Dynamic, yet inertial – and definitely futuristic

Researchers conduct experiments to demonstrate inertial motion in magnetic materials

In the journal Nature Physics (DOI: 10.1038/s41567-020-01040-y), an international team of scientists from Germany, Italy, Sweden, and France report on their experimental observation of an inertial effect of electron spins in magnetic materials, which had previously been predicted, but difficult to demonstrate. The results are the outcome of one of the first long-term projects at the high-power terahertz light source TELBE at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR).

Today, most of the world’s “memory” is stored on magnetic data carriers – hard disks – without which our digital lives would be unthinkable. In the magnetic material, it is the electron spins that do the actual job of storing the data. Imagine this spin as electrons rotating around their own axes, either to the left or right – representing the digital “zeros” and “ones”.

There is something special about this rotation, as Dr. Jan-Christoph Deinert from the HZDR Institute of Radiation Physics explains: “In the magnetic field, the electron behaves like a tumbling spinning top. The rotational axis of the electron changes its direction on a circular path. We call this process precession. When disturbed by an external force, the rotational axis should also make small oscillatory movements, called nutation, which overlap the precession. Like precession, it is a characteristic of many rotating objects, from children’s spinning tops to planets like Earth. Due to its much smaller scale, however, nutation is far more difficult to observe.”

Read more on the Helzholtz Zentrum Dresden Rossendorf website

Image: An international team of scientists has managed for the first time to observe the ‘nutation’ of spins in magnetic materials (the oscillations of their axis during precession). Foto: Dunia Maccagni

Seven at one pulse

Seven at one pulse

New material acts as an efficient frequency multiplier

Higher frequencies mean faster data transfer and more powerful processors – the formula that has been driving the IT industry for years. Technically, however, it is anything but easy to keep increasing clock rates and radio frequencies. New materials could solve the problem. Experiments at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have now produced a promising result: An international team of researchers was able to get a novel material to increase the frequency of a terahertz radiation flash by a factor of seven: a first step for potential IT applications, as the group reports in the journal Nature Communications (DOI: 10.1038/s41467-020-16133-8).

Read more on the TELBE at Helmholtz-Zentrum Dresden-Rossendorf website

Image: An international team of researchers was able to show that the three-dimensional Dirac material cadmium arsenide (blue-red cone) can multiply the frequency of a strong terahertz pulse (red line) by a factor of seven. The reason for this are the free electrons (red dots) in the cadmium arsenide, which are accelerated by the electrical field of the terahertz flash and, thus, in turn emit electromagnetic radiation.

Credit: HZDR / Sahneweiß / istockphoto.com, spainter_vfx

A closer look at superconductors

A closer look at superconductors

A new measuring method helps understand the physics of high-temperature superconductivity

From sustainable energy to quantum computers: high-temperature superconductors have the potential to revolutionize today’s technologies. Despite intensive research, however, we still lack the necessary basic understanding to develop these complex materials for widespread application. “Higgs spectroscopy” could bring about a watershed as it reveals the dynamics of paired electrons in superconductors. An international research consortium centered around the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Max Planck Institute for Solid State Research (MPI-FKF) is now presenting the new measuring method in the journal Nature Communications (DOI: 10.1038/s41467-020-15613-1). Remarkably, the dynamics also reveal typical precursors of superconductivity even above the critical temperature at which the materials investigated attain superconductivity.

Read more on the TELBE at HZDR website

Image: Deciphering previously invisible dynamics in superconductors – Higgs spectroscopy could make this possible: Using cuprates, a high-temperature superconductor, as an example, an international team of researchers has been able to demonstrate the potential of the new measurement method. By applying a strong terahertz pulse (frequency ω), they stimulated and continuously maintained Higgs oscillations in the material (2ω). Driving the system resonant to the Eigenfrequency of the Higgs oscillations in turn leads to the generation of characteristic terahertz light with tripled frequency (3ω).

A laser for penetrating waves

A laser for penetrating waves

Research team develops a new principle to generate terahertz radiation

The “Landau-level laser” is an exciting concept for an unusual radiation source. It has the potential to efficiently generate so-called terahertz waves, which can be used to penetrate materials as well as for future data transmission. So far, however, nearly all attempts to make such a laser reality have failed. An international team of researchers has now taken an important step in the right direction: In the journal Nature Photonics (DOI: 10.1038/s41566-019-0496-1), they describe a material that generates terahertz waves by simply applying an electric current. Physicists from the German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) played a significant role in this project.
Like light, terahertz waves are electromagnetic radiation, in a frequency range between microwaves and infrared radiation. Their properties are of great technological and scientific interest, as they allow fundamental researchers to study the oscillations of crystal lattices or the propagation of spin waves. Simultaneously “terahertz waves are of interest for technical applications because they can penetrate numerous substances that are otherwise opaque, such as clothing, plastics and paper,” Stephan Winnerl from HZDR’s Institute of Ion Beam Physics and Materials Research explains. Terahertz scanners are already used today for airport security checks, detecting whether passengers are concealing dangerous objects under their clothing – without having to resort to harmful X-rays.
>Read more on the FELBE at HZDR website

Image: An international research team has been able to show that it is relatively easy to generate terahertz waves with an alloy of mercury, cadmium and tellurium. To examine the behavior of the electrons in the material, the physicists use the free-electron laser FELBE at HZDR. Circularly polarized terahertz pulses (orange spiral) excite the electrons (red) from the lowest to the next higher energy level (parabolic shell). The energy gap of these so-called Landau levels can be adjusted with the help of a magnetic field. Credit : HZDR / Juniks