3D laser nano-printing on fibre paves the way for super-focusing of multimode laser radiation

Grigorii S. Sokolovskii, Vasileia Melissinaki, Ksenia A. Fedorova, Vladislav V. Dudelev, Sergey N. Losev, Vladislav E. Bougrov, Wilson Sibbett, Maria Farsari, Edik U. Rafailov

Research output: Contribution to journalArticlepeer-review

Abstract

Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10–100 times greater than the diffraction limit. This inevitably restricts their wider use in ‘direct-diode’ applications in materials processing and biomedical photonics. We report here a ‘super-focusing’ characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a ‘needle’ beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the ‘direct-diode’ applications in material processing and 3D printing, where both high power and tight focusing is required.
Original languageEnglish
Article number14618
JournalScientific Reports
Volume8
Issue number1
DOIs
Publication statusPublished - 2 Oct 2018

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© The Author(s) 2018

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