One- and two-photon absorption in solution: The effects of a passive auxiliary beam

Ford, Jack; Andrews, Davıd L.

doi:10.1063/1.4887539

Cited by 7 publications

(9 citation statements)

References 31 publications

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“…The bulk isotropy of a free fluid is represented by applying an isotropic rotational average, in which each molecule is decoupled from the space-fixed frame into its own frame (a detailed description is found elsewhere [72]), equation (13)…”

Section: Isotropic and Partially Oriented Systemsmentioning

confidence: 99%

Chiral discrimination in optical trapping and manipulation

Bradshaw¹,

Andrews²

2014

New J. Phys.

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When circularly polarized light interacts with chiral molecules or nanoscale particles powerful symmetry principles determine the possibility of achieving chiral discrimination, and the detailed form of electrodynamic mechanisms dictate the types of interaction that can be involved. The optical trapping of molecules and nanoscale particles can be described in terms of a forward-Rayleigh scattering mechanism, with trapping forces being dependent on the positioning within the commonly non-uniform intensity beam profile. In such a scheme, nanoparticles are commonly attracted to local potential energy minima, ordinarily towards the centre of the beam. For achiral particles the pertinent material response property usually entails an electronic polarizability involving transition electric dipole moments. However, in the case of chiral molecules, additional effects arise through the engagement of magnetic counterpart transition dipoles. It emerges that, when circularly polarized light is used for the trapping, a discriminatory response can be identified between left-and righthanded polarizations. Developing a quantum framework to accurately describe this phenomenon, with a tensor formulation to correctly represent the relevant molecular properties, the theory leads to exact analytical expressions for the associated energy landscape contributions. Specific results are identified for liquids and solutions, both for isotropic media and also where partial alignment arises due to a static electric field. The paper concludes with a pragmatic analysis of the scope for achieving enantiomer separation by such methods.

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Section: Isotropic and Partially Oriented Systemsmentioning

confidence: 99%

Chiral discrimination in optical trapping and manipulation

Bradshaw¹,

Andrews²

2014

New J. Phys.

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“…The above analysis, illustrating derivation of the effect of the passive beam on single-photon absorption, has been extended in other previous work to apply to laser-modified two-photon absorption 7,8 . An alternative route to the same result is to determine corrections to the material wavefunctions resulting from the passive beam -as a second-order (dynamic) Stark effect -and then to use the corrected states as a basis for the normal calculation of single-photon absorption.…”

Section: Optical Catalysis Of Light-matter Processesmentioning

confidence: 97%

Passive laser irradiation as a tool for optical catalysis

Forbes

Andrews

2020

Nanophotonics VIII

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The mechanisms of absorption, emission, and scattering of photons form the foundations of optical interactions between light and matter. In the vast majority of such interactions there is a significant interplay and energy exchange between the radiation field and the material components. In absorption for example, modes of the field are depopulated by photons whose energy is at resonance with a molecular transition producing excited material states. In all such optical phenomena, the initial state of the radiation field differs in mode occupation to its final state. However, certain optical processes can involve off-resonance laser beams that are unchanged on interaction with the material: the output light, after interaction, is identical to the laser input. Such off-resonance interactions include forward Rayleigh scattering, responsible for the wellknown gradient force in optical trapping, and the laser-induced intermolecular interaction commonly termed optical binding; in both processes, an intense beam delivers its effect without suffering change. It is possible for beams detuned from resonance to provide not only techniques for optomechanical and optical manipulation, but also to passively influence other important and functional interactions such as absorption from a resonant beam, or energy transfer. Such effects can be grouped under the banner of 'optical catalysis', since they can significantly influence resonant processes. Furthermore, off-resonance photonics affords a potential to impact on chemical interactions, as in the passive modification of rotational constants and phase transitions. To date, apart from optical manipulation, the potential applicability of passive photonics, particularly in the realm of chemical physics and materials science, has received little attention. Here we open up this field, highlighting the distinct and novel role that off-resonance laser beams and the ensuing photonics can play.

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“…(13); thorough detail of this procedure can be found in Ref. [47]. The first term involves a simple second-rank rotational average, giving…”

Section: Orientational Effects Of the Input Beam A Ensemble Averagesmentioning

confidence: 99%

Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam

Andrews¹

2015

J. Opt. Soc. Am. B

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The photonic interaction generally responsible for the electromagnetic trapping of molecules is forward-Rayleigh scattering, a process that is mediated by transition electric dipoles connecting the ground electronic state and virtual excited states. Higher order electric and magnetic multipole contributions to the scattering amplitude are usually negligible. However, on consideration of chiral discrimination effects (in which an input light of left-handed circular polarization can present different observables compared to right-handed polarization, or molecules of opposite enantiomeric form respond differently to a set circular polarization), the mechanism must be extended to specifically accommodate transition magnetic dipoles. Moreover, it is important to account for the fact that chiral molecules are necessarily nonspherical, so that their interactions with a laser beam will have an orientational dependence. Using quantum electrodynamics, this article quantifies the extent of the energetic discrimination that arises when chiral molecules are optically trapped, placing particular emphasis on the orientational effects of the trapping beam. An in-depth description of the intricate ensemble-weighted method used to incorporate the latter is presented. It is thus shown that, when a mixture of molecular enantiomers is irradiated by a continuous beam of circularly polarized light, a difference arises in the relative rates of migration of each enantiomer in and out of the most intense regions of the beam. As a consequence, optical trapping can be used as a means of achieving enantiomer separation.

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One- and two-photon absorption in solution: The effects of a passive auxiliary beam

Cited by 7 publications

References 31 publications

Chiral discrimination in optical trapping and manipulation

Chiral discrimination in optical trapping and manipulation

Passive laser irradiation as a tool for optical catalysis

Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam

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