Hyper-Rayleigh scattering in centrosymmetric systems
TL;DR: The detailed derivation in this work leads to results which are summarized for perpendicular detection of polarization components both parallel and perpendicular to the pump radiation, leading to distinct polarization ratio results, as well as a reversal ratio for forward scattered circular polarizations.
Abstract: Hyper-Rayleigh scattering (HRS) is an incoherent mechanism for optical second harmonic generation. The frequency-doubled light that emerges from this mechanism is not emitted in a laser-like manner, in the forward direction; it is scattered in all directions. The underlying theory for this effect involves terms that are quadratic in the incident field and involves an even-order optical susceptibility (for a molecule, its associated hyperpolarizability). In consequence, HRS is often regarded as formally forbidden in centrosymmetric media. However, for the fundamental three-photon interaction, theory based on the standard electric dipole approximation, representable as E13, does not account for all experimental observations. The relevant results emerge upon extending the theory to include E12M1 and E12E2 contributions, incorporating one magnetic dipolar or electric quadrupolar interaction, respectively, to a consistent level of multipolar expansion. Both additional interactions require the deployment of higher orders in the multipole expansion, with the E12E2 interaction analogous in rank and parity to a four-wave susceptibility. To elicit the correct form of response from fluid or disordered media invites a tensor representation which does not oversimplify the molecular components, yet which can produce results to facilitate the interpretation of experimental observations. The detailed derivation in this work leads to results which are summarized for the following: perpendicular detection of polarization components both parallel and perpendicular to the pump radiation, leading to distinct polarization ratio results, as well as a reversal ratio for forward scattered circular polarizations. The results provide a route to handling data with direct physical interpretation, to enable the more sophisticated design of molecules with sought nonlinear optical properties.
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TL;DR: In this article, a broad guide to cutting-edge applications of quantum electrodynamics is provided, providing an outline of its underlying foundation and an examination of its role in photon science.
Abstract: One of the key frameworks for developing the theory of light–matter interactions in modern optics and photonics is quantum electrodynamics (QED). Contrasting with semiclassical theory, which depicts electromagnetic radiation as a classical wave, QED representations of quantized light fully embrace the concept of the photon. This tutorial review is a broad guide to cutting-edge applications of QED, providing an outline of its underlying foundation and an examination of its role in photon science. Alongside the full quantum methods, it is shown how significant distinctions can be drawn when compared to semiclassical approaches. Clear advantages in outcome arise in the predictive capacity and physical insights afforded by QED methods, which favors its adoption over other formulations of radiation–matter interaction.
36 citations
TL;DR: In the wide realm of applications of quantum electrodynamics, a non-covariant formulation of theory is particularly well suited to describing the interactions of light with molecular matter, and a variety of symmetry principles are drawn out with reference to applications.
Abstract: In the wide realm of applications of quantum electrodynamics, a non-covariant formulation of theory is particularly well suited to describing the interactions of light with molecular matter The robust framework upon which this formulation is built, fully accounting for the intrinsically quantum nature of both light and the molecular states, enables powerful symmetry principles to be applied With their origins in the fundamental transformation properties of the electromagnetic field, the application of these principles can readily resolve issues concerning the validity of mechanisms, as well as facilitate the identification of conditions for widely ranging forms of linear and nonlinear optics Considerations of temporal, structural, and tensorial symmetry offer significant additional advantages in correctly registering chiral forms of interaction More generally, the implementation of symmetry principles can considerably simplify analysis by reducing the number of independent quantities necessary to relate to experimental results to a minimum In this account, a variety of such principles are drawn out with reference to applications, including recent advances Connections are established with parity, duality, angular momentum, continuity equations, conservation laws, chirality, and spectroscopic selection rules Particular attention is paid to the optical interactions of molecules as they are commonly studied, in fluids and randomly organised media
18 citations
Cites background from "Hyper-Rayleigh scattering in centro..."
...The associated ‘J’ and ‘K’ tensors molecular tensors retain index permutational symmetry if the M1 or E2 interaction is involved in the output emission, but not if it is linked with one of the two input photon annihilation events [80,81]....
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TL;DR: This work presents a rigorous quantum electrodynamical analysis of the scattering process, involving a partially index-symmetric construction of the fourth-rank γ tensor-dispensing with the Kleinman symmetry condition.
Abstract: Third-harmonic scattering is a nonlinear optical process that involves the molecular second-hyperpolarizability, γ. This work presents a rigorous quantum electrodynamical analysis of the scattering process, involving a partially index-symmetric construction of the fourth-rank γ tensor—dispensing with the Kleinman symmetry condition. To account for stochastic molecular rotation in fluids, methods of isotropic averaging must be employed to relate the molecular properties to accessible experimental quantities such as depolarization ratio. A complete eighth-rank tensor rotational average yields results for observable third-harmonic scattering rates, cast as a function of the natural-invariant γ components, and the polarization geometry of the experiment. Decomposing the tensor γ into irreducible weights allows specific predictions to be made for each molecular point group, allowing greater discrimination between the results for different molecular symmetries.
15 citations
TL;DR: In this paper, six water-soluble bications, characterized by a symmetric A+-π-D-π+A+ structure, were synthesized and comprehensively studied for their absorption and fluorescence properties, and their nonlinear optical response.
12 citations
TL;DR: In this article, a detailed quantum electrodynamical analysis highlights a mechanism exhibiting the possibility of a delocalized origin for paired output photons: the spatial extent of the region from which the pair is generated can be much larger than previously thought.
Abstract: The generation of correlated photon pairs is a key to the production of entangled quantum states, which have a variety of applications within the area of quantum information. In spontaneous parametric down-conversion—the primary method of generating correlated photon pairs—the associated photon annihilation and creation events are generally thought of as being colocated: The correlated pair of photons is localized with regards to the pump photon and its positional origin. A detailed quantum electrodynamical analysis highlights a mechanism exhibiting the possibility of a delocalized origin for paired output photons: The spatial extent of the region from which the pair is generated can be much larger than previously thought. The theory of both localized and nonlocalized degenerate down-conversion is presented, followed by a quantitative analysis using discrete-volume computational methods. The results may have significant implications for quantum information and imaging applications, and the design of nonlinear optical metamaterials.
6 citations
Cites background from "Hyper-Rayleigh scattering in centro..."
...Higher-order couplings that occur outside the electric-dipole approximation become significant when studying chiral discriminatory effects in optical processes including forces [70] and nonlinear optics [71,72]....
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TL;DR: In this article, the authors show that the intrinsic hyperpolarizability of poly(phenanthrene) is the highest ever measured, breaking the longstanding apparent limit, and that the linear and nonlinear optical properties of the polymer depend strongly on solvent conditions, affecting the macromolecular organization.
Abstract: Disubstituted poly(phenanthrene), a conjugated polymer, has been studied by hyper-Rayleigh scattering. Although this compound lacks the donor–acceptor motif that is typically associated with a strong second-order nonlinear optical response, the (intrinsic) hyperpolarizability ranks among the highest ever measured, breaking the longstanding apparent limit. The linear and nonlinear optical properties of the polymer depend strongly on the solvent conditions, affecting the macromolecular organization. An explanation for these unexpected results is postulated and is based on modulation of conjugation along the polymer backbone. As the molecular structure of the compound does not at all fit into the classical paradigms, our observations put these theories into perspective.
16 citations
TL;DR: The problem of non-linear scattering of unpolarized light is discussed in this article, where the authors show that the usual equation connecting the depolarization ratios for plane and unpolarised light does not hold for nonlinear scattering processes such as hyper-Rayleigh and hyper-Raman scattering.
12 citations
TL;DR: In this paper, a theory cast directly in terms of the observable, the harmonic intensity, to resolve the issue of coherent and incoherent second harmonic generation is proposed. But it is not clear whether the theory is applicable to the case of surface or interface of isotropic fluids.
Abstract: Use of the classical polarization concept is deeply entrenched in standard nonlinear optics. Nonetheless it establishes a framework for the formulation of theory which is not directly amenable to the resolution of certain kinds of question. In particular, it can obscure the difference between coherent and incoherent optical response. This has been forcefully illustrated by recent controversy over the issue of second harmonic generation involving surfaces or interfaces of isotropic fluids. It is the purpose of this paper, by formulating a theory cast directly in terms of the observable, the harmonic intensity, to resolve the issue. Through a unified treatment of both coherent and incoherent contributions to the second harmonic, it is unequivocally demonstrated that any signal classically associated with longitudinal polarization is necessarily incoherent.
12 citations
TL;DR: In this article, the reversal ratio in double-photon scattering (DPhS) has been used for direct determination of the anisotropy of nonlinear polarizability in molecules without a center of symmetry.
9 citations
TL;DR: In this article, the authors apply the theory of molecular quantum electrodynamics to the calculation of the matrix element, transition rate, and integrated signal intensity for sum-frequency and second-harmonic generation taking place in a chiral liquid in the presence and absence of a static electric field, to examine which coherent and incoherent processes exist in the electric-dipole approximation in liquids.
Abstract: Coherent second-order nonlinear optical processes are symmetry forbidden in centrosymmetric environments in the electric-dipole approximation. In liquids that contain chiral molecules, however, and which therefore lack mirror image symmetry, coherent sum-frequency generation is possible, whereas second-harmonic generation remains forbidden. Here we apply the theory of molecular quantum electrodynamics to the calculation of the matrix element, transition rate, and integrated signal intensity for sum-frequency and second-harmonic generation taking place in a chiral liquid in the presence and absence of a static electric field, to examine which coherent and incoherent processes exist in the electric-dipole approximation in liquids. Third- and fourth-order time-dependent perturbation theory is employed in combination with single-sided Feynman diagrams to evaluate two contributions arising from static field-free and field-induced processes. It is found that, in addition to the coherent term, an incoherent proc...
9 citations