Multicolored light twists new knotted ways


Multicolored light twists new knotted ways

ICFO researchers who participated in the studies. From left to right: Gerard Jiménez Machado, Juan P. Torres, Veronica Vicuña Hernandez, Emilio Pisanty and Maciej Lewenstein. Credit: ICFO

Around the age of six, we begin to learn to tie our laces by making knots that look like ribbons, or even more complex shapes, if we are a bit clumsy. We use nodes every day, but the type of nodes we usually use is associated with physical objects, things we can touch.

Although it may be difficult to visualize, the light may also be shaped to form knotted configurations, the shape of which depends on the orbital angular momentum of the light. This parameter is responsible for twisting the light beam around its own axis, generating different forms of nodes and developing a new degree of freedom capable of carrying valuable information.

Learning to master how to generate a twisted light – light with kinetic orbital momentum – is a field of study in full swing for 20 years. Unlike the angular moment of spin, which is associated with the polarization of light, the orbital angular momentum is associated with the spatial distribution of the electric field. These two types of kinetic moment can also be coupled, resulting in a variety of light fields of different shapes with polarizations that change from point to point.

The behavior of the light also becomes richer when it passes from oscillation at a single frequency (monochromatic light) to a different vibration frequency. This introduces a wide range of polarization states, each describing a shape that can be traced by the electric field of light over time. The combination of this larger space of possibilities with the spatial variations produced by the orbital angular momentum should leave even more room for interesting connections, but this boundary was so far unknown: although there is much research on the structured light, mainly focused on monochrome fields.

In a recent study, published in two articles, joint collaborations of ICFO researchers have allowed to break through the theoretical and experimental ground in this new field, discovering new types of nodes for twisted light and a new type of kinetic moment.

Multicolored light twists new knotted ways

Emilio Pisanty, ICFO researcher and lead author, presents pieces representing different node configurations. Credit: ICFO

In the first article, published in Photonic Nature, ICFO researchers Emilio Pisanty, Gerard Jiménez Machado, Veronica Vicuña Hernández, Antonio Picón and Alessio Celi, led by Professor ICREA at ICFO Maciej Lewenstein and Professor UPC at ICFO Juan P. Torres, designed a beam of light with a state of polarization that forms trefoil clovers at each point, combining a light of different frequencies (w and 2w) and connecting them so that the light beam is node-shaped .

These beams also present a new type of kinetic moment, associated with the unusual symmetry of the beams, which remain invariant during rotations – but only when the polarization is rotated by a specific fraction of the rotation of spatial dependence . They called this new quantity the angular momentum of the torus node, because of the type of node in the beams.

The researchers also experimentally implemented these beams, using nonlinear crystals to generate them, and designed a nonlinear polarization tomography scheme to measure clover shapes traced by the electric field. Their measurements show the presence of a new type of optical singularity, topologically protected and resistant to disturbances caused by the different orientation of the polarized clovers at different points around a circularly polarized center.

In the second article, published in Letters of physical examination, ICFO researchers Emilio Pisanty and Antonio Picón, led by Professor ICREA of ICFO Maciej Lewenstein, in collaboration with researchers from Laser Applications and Photonics at the University of Salamanca and CU Boulder, show that this new optical singularity can be applied to non-linear applications. optics, even at extremes of high intensity and in non-perturbative situations.

They show, by theoretical simulations, that the high-order harmonics produced by toric-node beams at very high intensities preserve the coordinated symmetry of the pilot laser, thus forming twisted spirals of very short pulses of light, and that the torus The kinetic moment -knot is preserved in the interaction. This new symmetry is essential to understand the production of very short wavelength shaping light, which can be used for new applications in microscopy, lithography and spectroscopy.

The results of both studies provide new frameworks and results that advance the study of structured light and nonlinear optics. On the one hand, researchers have been able to find new conservation laws for non-linear optics, which are valid even in extreme situations where tens or hundreds of photons are combined to form a single high-frequency photon. On the other hand, they analyzed the control fields that make this possible and showed that they contained a new optical singularity, with a new degree of freedom, that could be used to store valuable information, opening the opportunity to use these new light topologies for years to come. communication applications, among others.

Researchers use polarized light beams to engrave complex patterns on discs

More information:
Tying knots of fractional order with the state of polarization of light, Photonic Nature (2019). DOI: 10.1038 / s41566-019-0450-2,

Emilio Pisanty et al. Conservation of angular momentum at torus node in high order harmonic generation, Letters of physical examination (2019). DOI: 10.1103 / PhysRevLett.122.203201

The multicolored light twists in new paths knotted (June 10, 2019)
recovered on June 10, 2019

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