Tight Focal Spots Using Azimuthally Polarised Light From a Fresnel Cone

Hawley, R.D., Offer, R., Radwell, N. and Franke-Arnold, S. (2020) Tight Focal Spots Using Azimuthally Polarised Light From a Fresnel Cone. SPIE Photonics Europe 2020, 06-10 Apr 2020. ISBN 9781510634909 (doi:10.1117/12.2559535)

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When focusing a light beam at high numerical aperture, the resulting electric field profile in the focal plane depends on the transverse polarisation profile, as interference between different parts of the beam needs to be taken into account. It is well known that radial polarised light produces a longitudinal polarisation component and can be focused below the conventional diffraction limit for homogeneously polarised light, and azimuthally polarised light that carries one unit of angular momentum can achieve even tighter focal spots. This is of interest for example for enhancing resolution in scanning microscopy. There are numerous ways to generate such polarisation structures, however, setups can be expensive and usually rely on birefringent components, hence prohibiting broadband operation. We have recently demonstrated a passive, low-cost technique using a simple glass cone (Fresnel cone) to generate beams with structured polarisation. We show here that the polarisation structure generated by Fresnel cones focuses better than radial polarised light at all numerical apertures. Furthermore, we investigate in detail the application of polarised light structures for two-photon microscopy. Specifically we demonstrate a method that allows us to generate the desired polarisation structure at the back aperture of the microscope by pre-compensating any detrimental phase shifts using a combination of waveplates.

Item Type:Conference or Workshop Item
Glasgow Author(s) Enlighten ID:Franke-Arnold, Professor Sonja and Radwell, Dr Neal and Offer, Dr Rachel and Hawley, Mr Ryan
Authors: Hawley, R.D., Offer, R., Radwell, N., and Franke-Arnold, S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Copyright Holders:Copyright © 2020 SPIE
First Published:First published in Proceedings of SPIE 11359: 1135910
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
190841UK Quantum Technology Hub in Enhanced Quantum ImagingMiles PadgettEngineering and Physical Sciences Research Council (EPSRC)EP/M01326X/1P&S - Physics & Astronomy
190828EPSRC Centre for Doctoral Training in Sensing and MeasurementAndrew HarveyEngineering and Physical Sciences Research Council (EPSRC)EP/L016753/1P&S - Physics & Astronomy