Relevance of longitudinal fields of paraxial optical vortices

Forbes, Kayn A.; Green, Dale; Jones, G.

doi:10.1088/2040-8986/abff96

Cited by 35 publications

(28 citation statements)

References 56 publications

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“…We introduced an asymmetry parameter, δ , in the symmetric LG beam to obtain an asymmetric LG beam. We also consider the longitudinal component of the field (E z ) as a correction to the paraxial regime 51,52 to take into account its finite l (OAM) contribution. The importance of longitudinal component in light-matter interaction has been recently demonstrated in differentiating nanoparticle aggregates using helical light 26 .…”

Section: Asymmetric Laguerre-gaussian Beamsmentioning

confidence: 99%

Nonlinear helical dichroism in chiral and achiral molecules

et al. 2022

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Chiral interactions are prevalent in nature, driving a variety of bio-chemical processes. Discerning the two non-superimposable mirror images of a chiral molecule, known as enantiomers, requires interaction with a chiral reagent with known handedness. Circularly polarized light beams are often used as a chiral reagent. Here, we demonstrate efficient chiral sensitivity with linearly polarized helical light beams carrying an orbital angular momentum of ±lh, in which the handedness is defined by the twisted wavefront structure tracing a left-or right-handed corkscrew pattern as it propagates in space. By probing nonlinear optical response, we show that helicity dependent nonlinear absorption occurs even in achiral molecules and can be precisely controlled. We model this effect by considering induced multipole moments in light-matter interactions. Design and control of light-matter interactions with helical light opens new opportunities in chiroptical spectroscopy, light-driven molecular machines, optical switching, and in-situ ultrafast probing of chiral systems and magnetic materials.

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Section: Asymmetric Laguerre-gaussian Beamsmentioning

confidence: 99%

Nonlinear helical dichroism in chiral and achiral molecules

et al. 2022

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“…where ( ) The electric displacement field mode expansion for circularly-polarized Laguerre-Gaussian (LG) beams in the long Rayleigh range is given by [22]: (3) In Eq. ( 2) and Eq.…”

Section: Absorption Of Twisted Light By Chiral Particlesmentioning

confidence: 99%

“…a Gaussian mode) longitudinal fields only become important for very highly-focused non-paraxial laser fields and can be safely neglected for paraxial modes [20]. However, this is not the case for OAM-possessing paraxial optical vortex light, and in general first-order longitudinal fields of optical vortices should be included for beams with larger values of 0 kw than would be necessary for non-OAM paraxial posessing modes [21,22].…”

Section: Absorption Of Twisted Light By Chiral Particlesmentioning

confidence: 99%

“…What all these studies have in common however is that they assume the input beam is well-described as a paraxial vortex mode and fully transverse with respect to the direction of propagation. Under specific situations, however, longitudinal (in the direction of beam propagation) fields can become highly important, such as when the fields are stronglyfocused [20] or when specific angular momentum combinations are employed [21,22]. By accounting for longitudinal fields we highlight here a vortex dichroism (VD) which persists even for isotropic chiral particles in the dipole approximation.…”

Section: Introductionmentioning

confidence: 99%

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Optical vortex dichroism in chiral particles

Forbes

Jones

2021

Phys. Rev. A

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Circular dichroism is the differential rate of absorption of right-and left-handed circularly polarized light by chiral particles. Optical vortices which convey orbital angular momentum (OAM) possess a chirality associated with the clockwise or anti-clockwise twisting of their wavefront. Here it is highlighted that both oriented and randomly oriented chiral particles absorb photons from twisted beams at different rates depending on whether the vortex twists to the right or the left through a dipole coupling scheme. This is in contrast to previous studies that investigated dipole couplings with vortex modes in the paraxial approximation and showed no such chiral sensitivity to the vortex handedness: only in oriented media where electric quadrupole coupling contributes to optical activity effects due to absorption does such a mechanism exist for paraxial vortices. The distinct difference in the scheme highlighted in this work is that longitudinal fields are taken account of. Due to the vortex dichroism persisting in randomly oriented collections of chiral particles, the mechanism has a distinct advantage in its potential applicability in chemical and biochemical applications where the systems under study are invariably in the liquid phase. Additionally, the result is put into context in terms of the quantifiable optical chirality, highlighting that optical OAM can in fact increase the optical chirality density of an electromagnetic field.

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“…More generally, with the definition (13), optical SAM comprises not just conventional longitudinal spin angular momentum about the beam axis but also transverse spin. This is another consequence of non-zero longitudinal field components [83]; those field components and transverse spin are both neglected in the paraxial approximation [84,85]. In fact neither it nor the orbital AM operator satisfies the proper form of necessary quantum operator commutation [3,27]: instead, the following relations apply, where subscript indices denote Cartesian components, ε denotes the Levi-Civita antisymmetric tensor, and repeated indices require summation:…”

Section: Quantum Operatorsmentioning

confidence: 99%

Symmetry and Quantum Features in Optical Vortices

Andrews

2021

Symmetry

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Optical vortices are beams of laser light with screw symmetry in their wavefront. With a corresponding azimuthal dependence in optical phase, they convey orbital angular momentum, and their methods of production and applications have become one of the most rapidly accelerating areas in optical physics and technology. It has been established that the quantum nature of electromagnetic radiation extends to properties conveyed by each individual photon in such beams. It is therefore of interest to identify and characterize the symmetry aspects of the quantized fields of vortex radiation that relate to the beam and become manifest in its interactions with matter. Chirality is a prominent example of one such aspect; many other facets also invite attention. Fundamental CPT symmetry is satisfied throughout the field of optics, and it plays significantly into manifestations of chirality where spatial parity is broken; duality symmetry between electric and magnetic fields is also involved in the detailed representation. From more specific considerations of spatial inversion, amongst which it emerges that the topological charge has the character of a pseudoscalar, other elements of spatial symmetry, beyond simple parity inversion, prove to repay additional scrutiny. A photon-based perspective on these features enables regard to be given to the salient quantum operators, paying heed to quantum uncertainty limits of observables. The analysis supports a persistence in features of significance for the material interactions of vortex beams, which may indicate further scope for suitably tailored experimental design.

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Relevance of longitudinal fields of paraxial optical vortices

Cited by 35 publications

References 56 publications

Nonlinear helical dichroism in chiral and achiral molecules

Nonlinear helical dichroism in chiral and achiral molecules

Optical vortex dichroism in chiral particles

Symmetry and Quantum Features in Optical Vortices

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