At The Pulse Of A Light Wave

Physicists from the Attosecond Physics Laboratory at the LMU and the Max Planck Institute for Quantum Optics have developed a new type of detector with which the course of light waves can be precisely determined.

Light is fleeting. It spreads at almost 300,000 kilometers per second, its waves vibrate several million billion times per second. The distance between two wave crests of a light wave is less than one micrometer. Such an oscillation lasts less than three femtoseconds (a femtosecond is one millionth of a billionth of a second). If you want to work precisely with light and control it, you have to know it very well. So precisely that you know where and at what time individual wave peaks and valleys of light waves are located. Physicist from the Attosecond Physics Laboratory The LMU and the Max Planck Institute for Quantum Optics (MPQ) have now developed a novel detector that is able to measure the exact position of the light wave peaks of ultra-short infrared laser pulses.

This technology is important for investigations of the microcosm with the help of ultra-short laser pulses. Because it can be used to research the behavior of atoms and molecules. Laser pulses are used to stimulate particles in order to then “film” their movements in real time. However, this requires precise knowledge of the waveform of the laser pulses. The team of scientists led by physicist Dr. Boris Bergues and Prof. Dr. Matthias Kling , head of the research group "Ultrafast Imaging and Nanophotonics" at the LMU, has now made a decisive contribution. With its innovative detector, the so-called phase, i.e. the exact position of the wave crests, can be measured by each individual laser shot at a repetition rate of 10,000 shots per second.

To do this, the physicists first generate circularly polarized laser pulses in which the direction of the light field rotates like the hands of a clock, and then focus these rotating pulses in the ambient air. This creates a short current pulse, the direction of which depends on the exact location of the wave crest. The researchers then use the subsequent analysis of the exact direction of the current pulse to reconstruct the course of the light wave.

In contrast to conventional technology, for which a complex vacuum apparatus is required, the new method simply works in the ambient air and requires only a few components. "The simplicity of the measuring equipment promises that the method will become a new standard in laser technology," explains Matthias Kling.

"We think that the technology can be used at much higher repetition rates and in other wavelength ranges," says Boris Bergues. "Our technology is particularly promising for the characterization of short light pulses with high repetition rates, such as those generated on new laser infrastructures such as the European Light Infrastructure (ELI)," added Matthias Kling. Used on the most modern ultrashort pulse laser sources, the new light analysis technology could lead to technological breakthroughs as well as new knowledge about the behavior of particles in the microcosm. (LMU / MPQ) Optica 2020.