We examine the optical helicity, spin and ij-infra-zilches in electromagnetic theory show that these conserved quantities can be combined to form a new description of angular momentum associated with polarization: one is analogous familiar energy linear momentum. The symmetries Maxwell's equations underlie conservation our are presented discussed. explain similar but distinct set quantities, Lipkin's zilches, describe 'angular momentum' curl field, rather than field itself.

The modern field of optical angular momentum began with the realisation by Allen et al in 1992 that, addition to spin associated polarisation, light beams helical phase fronts carry orbital momentum. There has been much confusion and debate, however, surrounding intricacies and, particular, separation into its parts. Here we take opportunity state current position as understand it, which present six perspectives: (i) start a reprise paper it was pointed out that Laguerre–Gaussian modes,...

We suggest that the force F exerted upon a chiral molecule by light assumes form under appropriate circumstances, where and b pertain to whilst w h are local densities of electric energy helicity in optical field; gradients these quantities thus governing molecule's centre-of-mass motion. Whereas is identical for mirror-image forms or enantiomers molecule, has opposite signs; associated contribution therefore pointing directions. A simple field presented which vanishes but does not, so...

Works of music do not appear to be concrete objects; but they created by composers, and abstract objects seem the kind things that can created. In this paper I aim develop an ontological position lets us salvage creativity intuition without either adopting ontology abstracta or identifying musical works with concreta. will argue there are no in our ontology, nevertheless English sentences we want hold true literally true. rely on a meta-ontological view whereby ‘a exists’ committing entity...

The connection between magnetic field induced optical activity and chirality has a rich complicated history. Although the broken inversion symmetry of chiral molecules generates ‘natural’ activity, is generated by breaking time reversal symmetry. As result, molecular not expected to influence phenomena, such as Faraday rotation. Here we show that supramolecular assembly polymers can result in large effect. This strong rotation, which amongst highest value known for organic materials,...

Helicity is a familiar concept in particle physics and also appears the of fluids plasmas. In this paper, we present optical helicity form readily applicable to both quantum classical problems. We examine relationship between more spin show that conservation an expression electric-magnetic symmetry for light. distinct from Lipkin's 00-zilch; simple exists two only monochromatic fields. It has correct dimensions angular momentum, thereby accurately describing To illustrate physical...

In the absence of charges, Maxwell's equations are highly symmetrical. particular, they place electric and magnetic fields on equal footing. light this electric–magnetic symmetry, we introduce a variational description free electromagnetic field that is based upon acknowledgement both potentials. We use our description, together with Noether's theorem, to demonstrate symmetry is, in essence, an expression conservation optical helicity. The associated Lipkin's zilches also identified....

We suggest the use of certain readily producible types light to exert a force that points in opposite directions for enantiomers chiral molecule and propose multiple devices based upon this novel manifestation optical activity: particular, our discriminatory diffraction grating; device could be employed, example, measure enantiomeric excess sample molecules simply high precision. Our work is relevant many proposed may realizable using currently existing technology.

Chirality is exhibited by objects that cannot be rotated into their mirror images. It far from obvious this has anything to do with the angular momentum of light, which owes its existence rotational symmetries. There nevertheless a subtle connection between chirality and light. We demonstrate and, in particular, significance context chiral light-matter interactions.This article part themed issue 'Optical orbital momentum'.

This short review focuses on lichens which have cyanobacteria as their main photosynthetic partner or in localized areas termed cephalodia. Research is cited to show that cyanolichens are very sensitive gaseous air pollution, acid rain, and habitat disturbance. These worth conserving for own sake but also valuable assessing the status of forests like northeastern North America, where cover large tracts land. The richness cyanolichen flora reflects biological diversity forests. Cyanolichens...

In the strict absence of charge, it is manifestly possible to introduce two potentials in electrodynamics, one which well known and can be said magnetic character whilst other rather less electric character. Remarkably, both make explicit seemingly natural appearances fundamental description angular momentum freely propagating light. present paper, we review examine 'second potential' and, particular, consider its significance presence charge.

The relationship between lichen species richness and forest age was explored in southwestern Nova Scotia by examining the epiphytic lichens 51 conifer-dominated stands with no evidence of harvesting. stand ages were determined tree cores ranged from 52 to 292 years. One hundred thirty-five 61 genera identified, which 25 are new records for Scotia, two appear be science. Using Department Natural Resources' thresholds, 12 135 found exclusively “early old-growth” 16 only “advanced stands. These...

Helicity is a property of light which familiar from particle physics but less well-known in optics. In this paper we recall the explicit form taken by helicity within classical electromagnetic theory and reflect upon some its remarkable characteristics. The related to, distinct from, spin light. To emphasise fact, draw simple analogy between electric charge current. We illustrate other observations examining various superpositions plane waves explicitly.

• Premise of this study: Aquatic cyanolichens from the genus Peltigera section Hydrothyriae are subject to anthropogenic threats and, therefore, considered endangered. In study we addressed phylogenetic placement within . We delimited species and identified their symbiotic cyanobacteria. Methods: Species delimitation population structure were explored using monophyly as a grouping criterion (RAxML) Structurama based on three protein‐coding genes in combination with two nuclear ribosomal...

Mechanical interactions of chiral objects with their environment are well-established at the macroscale, like a propeller on plane or rudder boat. At colloidal scale and smaller, however, such often not considered deemed irrelevant due to Brownian motion. As we will show in this tutorial review, mechanical do have significant effects all scales, can be induced using shearing surfaces, collisions walls repetitive microstructures, fluid flows, by applying electrical optical forces. Achieving...

We introduce and examine a collection of unusual electromagnetic disturbances. Each these is an exact, monochromatic solution Maxwell's equations in free space with looped electric magnetic field lines finite extent localised appearance all three spatial dimensions. Included are the first explicit examples knots. also consider generation our disturbances laboratory, at both low high frequencies, highlight possible directions for future research, including use as basis new form...

Superpositions of coherent light waves typically interfere.We present superpositions up to six plane which defy this expectation by having a perfectly homogeneous mean square the electric field.For many applications in optics these can be seen as intensity.Our show interesting one-two-and three dimensional patterns their helicity densities, including several that support bright regions superchirality.Our might used write chiral certain materials and, conversely, such basis an 'optical...

The usual description in basic electromagnetic theory of the linear and angular momenta light is centred upon identification Poynting's vector as momentum density its cross product with position, or azimuthal component, density. This seemingly reasonable approach brings it peculiarities, however, particular regards to separation into orbital spin contributions, which has sometimes been regarded contrived. In present paper, we observe that densities are not unique, leads us ask whether is,...