Cylindrical-vector beams are of increasing recent interest for their role in novel laser resonators and their applications to electron acceleration and scanning microscopy. In this paper, we calculate cylindrical-vector fields, near the focal region of an aplanatic lens, and briefly discuss some applications. We show that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.

Focusing of high numerical aperture cylindrical-vector beams.

This chapter attempts to give an overview of the historical development and current progress of femtosecond laser micro-nanofabrication based on multiphoton absorption, and particular emphasis is placed on two-photon photopolymerization. Femtosecond laser interaction with matter differs essentially from those with longer pulses or CW lasers in its significant nonlinearity, ultrafast characteristics and the possibility of highly localization of reaction volume. These features enable three-dimensional (3D) micro-nanofabrication in solid and liquid media. In two-photon photopolymerization, when a near-infrared femtosecond laser is tightly focused into a photopolymerizable resin, 3D polymer micro-nanostructures are produced by pinpoint photopolymerization of liquid precursory resins. Using this direct laser writing scheme, various photonic, micro-optical components and micromechanical devices have been readily produced. The two-photon photopolymerization technology is expected to play a similar role to that played by lithography for planar semiconductor device processing, but for micro-nanofabrication of 3D polymer-based optoelectronic devices as well for microelectromechanical systems.

/pdf/two-photon-photopolymerization-and-3d-lithographic-2yer63az6z.pdf

Two-photon photopolymerization and 3D lithographic microfabrication

Super-resolution localization microscopy methods provide powerful new capabilities for probing biology at the nanometer scale via fluorescence. These methods rely on two key innovations: switchable fluorophores (which blink on and off and can be sequentially imaged) and powerful localization algorithms (which estimate the positions of the fluorophores in the images). These techniques have spurred a flurry of innovation in algorithm development over the last several years. In this Review, we survey the fundamental issues for single-fluorophore fitting routines, localization algorithms based on principles other than fitting, three-dimensional imaging, dipole imaging and techniques for estimating fluorophore positions from images of multiple activated fluorophores. We offer practical advice for users and adopters of algorithms, and we identify areas for further development.

Fluorophore localization algorithms for super-resolution microscopy

We review optical phenomena associated with the internal energy redistribution which accompany propagation and transformations of monochromatic light fields in homogeneous media. The total energy flow (linear-momentum density, Poynting vector) can be divided into a spin part associated with the polarization and an orbital part associated with the spatial inhomogeneity. We give a general description of the internal flows in the coordinate and momentum (angular spectrum) representations for both nonparaxial and paraxial fields. This enables one to determine local densities and integral values of the spin and orbital angular momenta of the field. We analyse patterns of the internal flows in standard beam models (Gaussian, Laguerre–Gaussian, flat-top beam, etc), which provide an insightful picture of the energy transport. Emphasis is given to the singular points of the flow fields. We describe the spin–orbit and orbit–orbit interactions in the processes of beam focusing and symmetry breakdown. Finally, we consider how the energy flows manifest themselves in the mechanical action on probing particles and in the transformations of a propagating beam subjected to a transverse perturbation.

https://iopscience.iop.org/article/10.1088/2040-8978/13/5/053001/pdf

Internal flows and energy circulation in light beams

This paper examines the use of Gauss-Laguerre beams in STED microscopy. These types of beams are shown to have beneficial properties that can be utilised to generate stable, high quality STED beams resulting in an aberration-resilient generation volume. In this paper we obtain general expressions for Gauss-Laguerre beams being focused through a stratified medium and describe their optimization for STED microscopy purposes. Our results show that the circularly polarised, lowest order "dark" beam is the most beneficial for STED purposes.

The use of Gauss-Laguerre vector beams in STED microscopy

On the general properties of polarised light conventional and confocal microscopes

In this paper we develop the theory of confocal microscopes imaging small scatterers. Since scattering is a polarization dependent phenomenon we employ a full vectorial theory to treat this problem. This approach permits us to consider both imaging in high aperture systems as well as image formation in polarized light microscopy. We extend previous theories by including effects of the finite sized detector apertures. Numerical examples are presented for the most important cases. The results of the full vectorial theory are compared with those obtained from low aperture paraxial theory.

Theory for confocal and conventional microscopes imaging small dielectric scatterers

A theory for multiphoton fluorescence imaging in high aperture scanning optical microscopes employing finite sized detectors is presented. The effect of polarisation of the fluorescent emission on the imaging properties of such microscopes is investigated. The lateral and axial resolutions are calculated for one-, two- and three-photon excitation of p-quaterphenyl for high and low aperture optical systems. Significant improvement in lateral resolution is found to be achieved by employing a confocal pinhole. This improvement increases with the order of the multiphoton process. Simultaneously, it is found that, when the size of the pinhole is reduced to achieve the best possible resolution, the signal-to-noise ratio is not degraded by more than 30%. The degree of optical sectioning achieved is found to improve dramatically with the use of confocal detection. For two- and three-photon excitation axial full width half-maximum improvement of 30% is predicted.

P. D. Higdon

Papers

On the general properties of polarised light conventional and confocal microscopes

Theory for confocal and conventional microscopes imaging small dielectric scatterers

Imaging properties of high aperture multiphoton fluorescence scanning optical microscopes

The imaging of dielectric point scatterers in conventional and confocal polarisation microscopes

Optimising the image contrast of conventional and confocal optical microscopes imaging finite sized spherical gold scatterers