Optical Magnetic Lens: towards actively tunable terahertz optics

TL;DR

This paper introduces a novel tunable optical magnetic lens (OML) that uses magneto-optical materials and magnetic fields to dynamically adjust focus across a broad frequency range, including terahertz, enabling ultrafast beam shaping.

Contribution

The paper presents the concept of a tunable OML based on magneto-optical materials, achieving rapid focal length tuning from microwaves to visible light, which surpasses fixed-geometry metasurface limitations.

Findings

OML operates across microwave to visible frequencies.

Achieves 50% relative tunability of focal length in terahertz range.

Enables ultrafast focus adjustment on picosecond timescales.

Abstract

As we read this text, our eyes dynamically adjust the focal length to keep the line image in focus on the retina. Similarly, in many optics applications the focal length must be dynamically tunable. In the quest for compactness and tunability, flat lenses based on metasurfaces were introduced. However, their dynamic tunability is still limited because their functionality mostly relies upon fixed geometry. In contrast, we put forward an original concept of a tunable Optical Magnetic Lens (OML) that focuses photon beams using a subwavelength-thin layer of a magneto-optical material in a non-uniform magnetic field. We applied the OML concept to a wide range of materials and found out that the effect of OML is present in a broad frequency range from microwaves to visible light. For terahertz light, OML can allow 50% relative tunability of the focal length on the picosecond time scale, which is of practical interest for ultrafast shaping of electron beams in microscopy. The OML based on magneto-optical natural bulk and 2D materials may find broad use in technologies such as 3D optical microscopy and acceleration of charged particle beams by THz beams.