Ultra-short light pulses in the shape of a wind-up toy put a new spin on photonics

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Synthesize spatiotemporal beams with broadband spectral topological correlations. Credit: Photonics of nature (2023). DOI: 10.1038/s41566-023-01223-y

We’ve all played with a spring toy at least once, but did you know that even light can be shaped like a spring?

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An international team of researchers, led by Marco Piccardo, former researcher at the Italian Institute of Technology (IIT) and now Professor at the Physics Department of Tcnico Lisboa and Principal Investigator at the Institute of Engineering for Microsystems and Nanotechnologies ( INESC MN), exploited ultrafast optics and structured light to synthesize in the laboratory a new family of spatiotemporal light beams, known as light sources.

The research was conducted in collaboration between IIT, Politecnico di Milano and Tcnico Lisboa. The discovery has disruptive potential for applications in photonics with complex light, such as time-resolved microscopy (useful, for example, to produce films describing the motion of molecules and viruses), laser-plasma acceleration and free space ( for example, in the atmosphere) optical communications.

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The research is published in Photonics of nature.

In ultrafast optics, it is possible to shorten or lengthen the duration of extremely short optical pulses down to a few femtoseconds, or thousandths of billionths of a second, or even produce complex pulses, using a technique known as pulse shaping. A central idea of ​​this principle is that the short laser pulses are composed of a wide range of colours.

Scientists separate a pulse into its constituent colors, which are then separately manipulated and recombined, resulting in a new shape of the laser pulse. While pulse shaping allows the temporal profile of a pulse to be manipulated, there is another set of techniques known as wavefront shaping which allows for spatial structure to be given to light. Light designers have learned to combine these two methods to shape light simultaneously in space and time, bridging ultrafast optics and structured light for entirely new space-time applications.

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A paradigm shift in spatiotemporal light shaping

Reporting now in Photonics of nature, Piccardo and his collaborators have introduced a paradigm shift in spatiotemporal light shaping. Unlike conventional modelers that separate different colors along a colored stripe, researchers have now used a special type of diffraction grating with circular symmetry to create a round rainbow of colours.

This is an experiment anyone can try at home: Shining a flashlight on an old CD-ROM and taking a picture with your phone’s camera will capture a round rainbow. Now, replace the flashlight with an ultrashort laser pulse and the CD-ROM with a microstructured diffractive device fabricated in the nanofabrication cleanroom and you’re halfway through the experiment. The second part of the experiment is to use advanced holograms to structure the many colors of light into different corkscrew-shaped optical vortexes.

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“This results in a new family of spatiotemporal light beams, evolving on an ultrashort femtosecond timescale with a highly customizable and convoluted light structure,” said Marco Piccardo. “It opens up unprecedented design capabilities in photonics, with many spectral and structural components to address.”

The broadband nature of these new light beams poses new challenges for their characterisation, which the team overcame by developing a powerful reconstruction technique, called hyperspectral holography, which provides complete tomography of complex space-time structures.

“Our technique, which combines holography with Fourier transform spectroscopy, allows a complete characterization of the spatiotemporal profile of complex beams, enabling radically new applications in the study of light-matter interactions,” said Giulio Cerullo, professor at Politecnico of Milan and co-author of the study.

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The team showed the unprecedented control their space-time modeler allowed by customizing many properties of the light sources. A beautiful demonstration shows two of these springs dancing together in space and time.

‘We have discovered extremely interesting physics using these beams, which could lead us to a whole new generation of compact accelerators and plasma light sources. This technique is very exciting because it promises to bring these theoretical concepts to the laboratory and to trigger important advances in the laser-plasma physics,” said Jorge Vieira, professor at Tcnico Lisboa and co-author of the study.

Now that it is finally possible to synthesize these light sources in complete freedom in the laboratory, the next natural step will be to bring them into laser-plasma experiments.

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“This is a very challenging goal, but the nanophoton fabrication capabilities of INESC MN in Lisbon and the excellent plasma research teams of Tcnico represent an ideal ecosystem to pursue this ambitious research,” said Piccardo. “Combining these advanced space-time beams with intense nonlinear laser-matter interactions could have important fundamental and technological implications.”

More information:
Marco Piccardo et al, Broadband control of spectral topological correlations in spatiotemporal bundles, Photonics of nature (2023). DOI: 10.1038/s41566-023-01223-y

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About the magazine:
Photonics of nature

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Provided by Tcnico Lisboa

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