Light is often thought of in terms of radial polarization, but longitudinal polarization is also possible, and it has some intriguing possibilities for particle acceleration. Binary optics, combined with a high-numerical-aperture lens, is a potential route to achieving light with this unusual property.

/pdf/creation-of-a-needle-of-longitudinally-polarized-light-in-3lwohpkiab.pdf

Creation of a needle of longitudinally polarized light in vacuum using binary optics

Non-Gaussian beam profiles such as Bessel or an- nular beams enable novel approaches to modifying materials through laser-based processing. In this review paper, proper- ties, generation methods and emerging applications for non- conventional beam shapes are discussed, including Bessel, an- nular, and vortex beams. These intensity profiles have important implications in a number of technologically relevant areas includ- ing deep-hole drilling, photopolymerization and nanopatterning, and introduce a new dimension for materials optimization and fundamental studies of laser-matter interactions.

Bessel and annular beams for materials processing

The imaging properties of optical microscopes are often compromised by aberrations that reduce image resolution and contrast. Adaptive optics technology has been employed in various systems to correct these aberrations and restore performance. This has required various departures from the traditional adaptive optics schemes that are used in astronomy. This review discusses the sources of aberrations, their effects and their correction with adaptive optics, particularly in confocal and two-photon microscopes. Different methods of wavefront sensing, indirect aberration measurement and aberration correction devices are discussed. Applications of adaptive optics in the related areas of optical data storage, optical tweezers and micro/nanofabrication are also reviewed.

/pdf/adaptive-optics-in-microscopy-1quh73g6jx.pdf

Adaptive optics in microscopy

The advance of nanophotonics has provided a variety of avenues for light–matter interaction at the nanometer scale through the enriched mechanisms for physical and chemical reactions induced by nanometer-confined optical probes in nanocomposite materials. These emerging nanophotonic devices and materials have enabled researchers to develop disruptive methods of tremendously increasing the storage capacity of current optical memory. In this paper, we present a review of the recent advancements in nanophotonics-enabled optical storage techniques. Particularly, we offer our perspective of using them as optical storage arrays for next-generation exabyte data centers. The science and technology of nanophotonics can help dramatically increase the capacity of optical discs. After reviewing research into next-generation optical data storage, Min Gu, Xiangping Li and Yaoyu Cao from the Swinburne University of Technology in Australia have offered their perspective of the creation of exabyte-scale optical data centers. They report that developments in ’super-resolution recording‚, which allow a light-sensitive material to be exposed to a focal spot that is smaller than the diffraction limit of light, will allow the size of recorded bits to shrink to just a few nanometres in size. This would ultimately allow a single disk to store petabytes of data and thus constitute a key component in optical storage arrays for ultrahigh-capacity optical data centers.

/pdf/optical-storage-arrays-a-perspective-for-future-big-data-44jjkj4x6j.pdf

Optical storage arrays: a perspective for future big data storage

Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry in a turbulent atmosphere is investigated. Analytical formulas for the average intensity of various DHBs prop ...

Propagation of various dark hollow beams in a turbulent atmosphere

We report on, in this letter, a phenomenon that the central zero-intensity point of a doughnut beam, caused by phase singularity, disappears in the focus, when such a beam is focused by a high numerical-aperture objective in free space. In addition, the focal shape of the doughnut beam of a given topological charge exhibits the increased ring intensity in the direction orthogonal to the incident polarization state and an elongation in the polarization direction. These phenomena are caused by the effect of depolarization, associated with a high numerical-aperture objective, and become pronounced by the use of a central obstruction in the objective aperture.

https://researchbank.swinburne.edu.au/file/2a342a30-7c9c-4c84-b2dc-241bcbeb0f07/1/PDF (Published version).pdf

Focusing of doughnut laser beams by a high numerical-aperture objective in free space.

We present a novel technique for producing a doughnut laser beam by use of a liquid-crystal cell. It is demonstrated that the liquid-crystal cell exhibits an efficiency in energy conversion near 100%. One of the main advantages of this method is its capability of dynamic switching between a Gaussian mode and a doughnut mode of different topological charges. The liquid-crystal cell is also dynamically tunable over the visible and near-infrared wavelength range. These advantages make the device appealing for laser trapping methods used in single-molecule biomechanics and for optical guiding of cold atoms.

Generation of doughnut laser beams by use of a liquid-crystal cell with a conversion efficiency near 100%.

There has been an interest to understand the trapping performance produced by a laser beam with a complex wavefront structure because the current methods for calculating trapping force ignore the effect of diffraction by a vectorial electromagnetic wave. In this letter, we present a method for determining radiation trapping force on a micro-particle, based on the vectorial diffraction theory and the Maxwell stress tensor approach. This exact method enables one to deal with not only complex apodization, phase, and polarization structures of trapping laser beams but also the effect of spherical aberration present in the trapping system.

https://researchbank.swinburne.edu.au/file/87f1faee-55f6-4610-ad8a-bd077d5101ee/1/PDF (Published version).pdf

Exact radiation trapping force calculation based on vectorial diffraction theory.

A physical model is presented to understand and calculate trapping force exerted on a dielectric micro-particle under focused evanescent wave illumination. This model is based on our recent vectorial diffraction model by a high numerical aperture objective operating under the total internal condition. As a result, trapping force in a focused evanescent spot generated by both plane wave (TEM00) and doughnut beam (TEM* 01) illumination is calculated, showing an agreement with the measured results. It is also revealed by this model that unlike optical trapping in the far-field region, optical axial trapping force in an evanescent focal spot increases linearly with the size of a trapped particle. This prediction shows that it is possible to overcome the force of gravity to lift a polystyrene particle of up to 800 nm in radius with a laser beam of power 10 µW.

https://researchbank.swinburne.edu.au/file/77b01494-19b7-459a-bc8a-1fd9aad1c379/1/PDF (Published version).pdf

Trapping force and optical lifting under focused evanescent wave illumination.

The inadequacy of the optical trapping model based on ray optics in the case of describing the optical trapping performance of annular and doughnut laser beams is discussed. The inadequacy originates from neglecting the complex focused field distributions of such beams, such as polarization and phase, and thus leads to erroneous predictions of trapping force. Instead, the optical trapping model based on the vectorial diffraction theory, which considers the exact field distributions of a beam in the focal region, needs to be employed for the determination of the trapping force exerted on small particles. The theoretical predictions of such a trapping model agree with the experimentally measured results.

https://researchbank.swinburne.edu.au/file/eeff03e5-a8d6-478f-9488-dc31fc7c44bf/1/PDF (Published version).pdf

Djenan Ganic

Papers

Focusing of doughnut laser beams by a high numerical-aperture objective in free space.

Generation of doughnut laser beams by use of a liquid-crystal cell with a conversion efficiency near 100%.

Exact radiation trapping force calculation based on vectorial diffraction theory.

Trapping force and optical lifting under focused evanescent wave illumination.

Optical trapping force with annular and doughnut laser beams based on vectorial diffraction