Tailored Light Inspired by Nature

Photo of the fabrication procedure of a nondiffracting of a lightfield using a desired transversed caustic. (Source: A. Zannotti, WWU)

Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during propagation. This represents an immense challenge since light typically broadens during propa­gation via diffrac­tion. Propa­gation-invariant or non-diffracting light fields therefore do not seem possible at first glance. If it were possible to produce them, they would enable new appli­cations such as light disk micro­scopy or laser-based cutting, milling or drilling with high aspect ratios.

An inter­national research team from the Uni­versities of Birmingham, Marseille and Muenster has now succeeded for the first time to create arbitrary non­diffracting beams. “We imple­ment an approach inspired by nature, in which any desired inten­sity structure can be specified by its boundaries,” explains Cornelia Denz from the Institute of Applied Physics at the Univer­sity of Muenster. The researchers cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses: specta­cular ray structures named caustics. They are bright focus lines that overlap, and thereby building networks that can be exploited for non­diffracting propa­gation.

The team developed a method to use these caustics as a basis for the generation of arbitrary structures, and has thus created an intelligent mani­pulation of ray propa­gation. In this way, countless new types of laser beams can be formed on the micro­meter scale, opening up completely new perspec­tives in optical materials processing, multi­dimensional signal transmission or advanced high resolution imaging.

Only some years ago it was possible to realize a few light fields that exhibit these non-dif­fracting properties, even though the theoretical idea is older: Concentric ring structures like the Bessel beam could be produced in a propa­gation-invariant way. The theory predicts a whole class of beams whose trans­verse shape is generated on ellip­tical or parabolic tra­jectories and represent natural solutions of the wave equation. Although there has long been a need for such customized light beams with these pro­perties, they have hardly been produced experi­mentally because the invariance of the transverse intensity structure must be main­tained during propa­gation. (Source: U. Muenster)

Reference: A. Zannotti et al.: Shaping caustics into propagation-invariant light, Nat. Commun. 11, 3597 (2020); DOI: 10.1038/s41467-020-17439-3

Link: Center for Nonlinear Science (CeNoS), University of Muenster, Muenster, Germany

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