Control Over The Waveform

An international team of physicists from the attoworld team at LMU and the Max Planck Institute for Quantum Optics have succeeded in generating ultra-short mid-infrared pulses and precisely controlling the waveform.

Infrared light is a door opener for a variety of technological applications. It creates the prerequisites for specifically stimulating molecules to vibrate and for generating electrical signals in semiconductors. If you want to technically use the oscillation of electric fields from ultra-short light pulses, you first have to find out how to best control them. This works well in many wavelength ranges, but until now controlling and controlling light in the mid-infrared wavelength spectrum has been a challenge.

An international team of physicists from attoworld-Teams from the LMU, the Max Planck Institute for Quantum Optics (MPQ) and the Hungarian Center for Molecular Fingerprinting (CMF) have now succeeded in generating ultra-short mid-infrared pulses and precisely controlling the waveform, i.e. its electric field.

This opens up a whole new possibility of optical control for biomedical applications and for quantum electronics.

Stable laser system
The basis for the new mid-infrared source is a stabilized laser system that generates light pulses with a well-defined waveform in the adjacent near-infrared. The pulses consist of only one oscillation of the light wave and are therefore only a few femtoseconds long: If these are sent into a zinc-germanium-phosphite crystal, complex mixing processes can be used to generate long-wave infrared pulses. In this way, a very large coverage of the light spectrum from 1 to 12 microns could be achieved. The researchers were not only able to explain the underlying physics of the mixing processes, but also use the new concept to precisely control the oscillations of the generated mid-infrared light via the input parameters.

speed up electronics
This control can, for example, specifically trigger certain electronic processes in solids, which could be important in future electronic signal processing and extremely accelerate them. "You could therefore develop light-controlled electronics by controlling the light pulses," says Philipp Steinleitner , one of the three first authors of the study. "If opto-electronic components were to work at frequencies of the generated light, today's electronics could be accelerated by a factor of at least 1000."

The attoworld physicists pay particular attention to the use of the new light technology in the spectroscopy of molecules. When infrared light hits molecules, they begin to oscillate and emit characteristic light. In this way, one can find out which molecules are in a liquid, such as in human blood. "With our laser technology, we have significantly expanded the controllable wavelength range in the infrared," explains Nathalie Nagl , also the first author of the study. "The additional wavelengths that are now available give us the opportunity to analyze even more precisely how a mix of molecules is composed."

Improving medical diagnostics
In the attoworld group, the colleagues from the Broadband Infrared Diagnostics (BIRD) team headed by Mihaela Zigman and the CMF Research Team headed by Alexander Weigel are particularly interested in the knowledge of the existence of certain molecules in the blood. The teams are working on how to use molecular spectroscopy to identify distinctive signatures — known as fingerprints. These allow a disease such as cancer to be detected at an early stage by means of a blood test. Because if there is a tumor in an organism, the disease leads to small and extremely complex changes in the molecular composition of the blood. These must be discovered in order to enable early diagnosis of serious diseases in the future. This significantly increases the patient's chances of recovery.

"In the future, our laser technology will enable our colleagues to detect previously undetectable changes in specific biomolecules such as proteins or lipids," explains Maciej Kowalczyk, also the first author of the study. "It increases the reliability of future medical diagnostics using infrared laser technology."