Ultra-short flashes of light combined precisely and quickly

The technological significance of ultra-short flashes lasting less than a quadrillionth of a second is rapidly increasing. In laser sources, groups and pairs of flashes of light can be developed instead of separate flashes. Like the chemically bound atoms in a molecule, they are connected to each other and their short time intervals can hold extraordinary stability.

Ultra-short flashes of light can be precisely combined, separating quickly in a quadrillionth of a second.
Ultra-short solitons overlay and produce spectral interference patterns: Real-time spectroscopy resolves their rapid dynamics and tracks the switching of soliton molecules in a femtosecond fiber laser. The image shows successive experimental spectra recorded during a switching process. Image credit: Moritz B. Heindl

Researchers at the universities of Bayreuth and Constance have recently discovered a cause for the unshakable coupling of ultra-short flashes of light and learned a method to regulate their distance both quickly and accurately. They describe their research results in the journal OPTICAL.

Flashing lights shorter than a quadrillionth of a second are also known as femtosecond pulses. Currently, they are used to study energy materials, such as precision scalps in medicine or in 3D manufacturing of parts.

These flashes in lasers are formed as solitons that can be defined as stable packets of light waves. The discovery of their coupling, which has currently been published, was acquired on a laser resonator. This includes a ring of fiberglass that allows the solitons to flow indefinitely.

In those systems, frequently coupled femtosecond flashes, so-called soliton molecules, are frequently seen. Using high-resolution real-time spectroscopy, the researchers succeeded in tracking the dynamics of two coupled flashes instantly in hundreds of thousands of circuits.

Based on these data, the researchers were able to demonstrate that it is optical reflections in the laser resonator that couple the separate solitons in space and time. The binding distances could be projected on the basis of transit time differences in the resonator and could finally be precisely adjusted by changing optical elements.

In addition, the new research shows how the bond between two blinks could be quickly loosened and a new bond formed. It is currently possible, for example, to accurately switch back and forth between flashes of light that occur in pairs and have different time intervals.

Based on our research results, it is now possible to switch soliton molecules at the touch of a button. This opens up new perspectives for the technical application of femtosecond pulses, especially in the field of spectroscopy and material processing.

Luca Nimmesgern B.Sc., Study First Author and Physics Master Student, University of Bayreuth

The results obtained by the laser resonator can be transmitted to a variety of ultra-short pulse laser sources. Consequently, it is possible to produce coupled flashes of light in other laser systems and easily change their distances.

Since the first reports of pulse pairs in fiber lasers more than 20 years ago, various explanations for the stability of soliton molecules in lasers have been proposed. The usual models have been contradicted by numerous observations, but are still used today.

Georg Herink, Research Coordinator and Junior Professor of Ultrafast Dynamics, University of Bayreuth

“Our new study now offers an accurate explanation that is compatible with the measured data for the first time. In a way, it provides a piece of the puzzle that makes a wealth of previous data understandable. Now complex laser physics can be used specifically to generate soliton high-speed sequences. “ added Herink.

The research group led by Dr. Alfred Leitenstorfer from the University of Konstanz has been involved in the creation of fiber lasers as a tool for spectroscopy for years.

Based on our new results, we can look forward to the realization of versatile technological applications.

Dr. Alfred Leitenstorfer, co-author and professor, University of Konstanz

Recently, a DFG research project at the University of Bayreuth began with the aim of understanding the interactions between ultra-short solitons in laser sources exhaustively and making them practical for laser applications in the future.

Journal reference:

Nimmesgern, L., et al. (2021) Soliton molecules in femtosecond fiber lasers: universal binding mechanism and direct electronic control. OPTICAL. doi.org/10.1364/OPTICA.439905.

Source: https://www.uni-bayreuth.de/en

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