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

2018; Nature Portfolio; Volume: 8; Issue: 1 Linguagem: Inglês

10.1038/s41598-018-32970-6

2045-2322

G. S. Sokolovskiĭ, Vasileia Melissinaki, Ksenia A. Fedorova, V. V. Dudelev, S. N. Losev, V.E. Bougrov, Wilson Sibbett, Maria Farsari, Edik U. Rafailov,

Optical Coherence Tomography Applications

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.