arXiv subjects

Calvin M. Hooper

Publications and source records attributed to Calvin M. Hooper.

5 recordsLinked to original sources

arXiv2026

Observation of symmetry breaking in time-varying scattering systems

From the Higgs mechanism to magnetic ordering, spontaneous symmetry breaking organizes physics across scales. Whether an analogous transition governs waves scattered by periodically driven structures has remained an open experimental challenge. Here we demonstrate a universal symmetry-breaking transition in a periodically driven finite scattering system. By measuring the multispectral Floquet scattering matrix of a strongly modulated microwave resonator, we observe a transition from an unbroken symmetry regime with scattering eigenvalues of equal modulus to a broken symmetry regime where their moduli split apart, through an exceptional point. At parametric resonance, this transition culminates in coherent perfect absorption, where a tailored multispectral input state is completely absorbed without outgoing radiation, the singular limit of the underlying transition. Because it arises from the general algebraic structure of the Floquet scattering matrix rather than from implementation-specific details, this transition should occur broadly in such systems. Unlike instability phenomena in bulk driven media, it emerges in the eigenstructure of a finite scattering operator that couples waves across multiple frequency channels. Our results establish Floquet scattering as an experimentally accessible platform for the observation of symmetry breaking and for dynamic wave control in driven photonic systems.

physics.optics↗

arXiv2025

Scattering in Time-Varying Drude-Lorentz Models

Motivated by recent experiments, the theoretical study of wave propagation in time varying materials is of current interest. Although significant in nearly all such experiments, material dispersion is commonly neglected in theoretical studies. Yet, as we show here, understanding the precise microscopic model for the material dispersion is crucial for predicting experimental outcomes. Here we study the temporal scattering coefficients of four different time-varying Drude-Lorentz models, exploring how an incident continuous wave splits into forward and backward waves due to an abrupt change in plasma frequency. The differences in the predicted scattering are unique to time-varying media, and arise from the exact way in which the time variation appears in the various model parameters. We verify our results using a custom finite difference time domain algorithm, concluding with a discussion of the limitations that arise from using these models with an abrupt change in plasma frequency.

physics.optics↗

arXiv2025

Quasi Normal Modes in Dispersive Photonic Time-Crystals

Quasinormal modes characterise the transient response of static optical cavities. Here, we introduce the notion of a Floquet quasinormal mode to describe transient responses in photonic time crystals. Contrasting their static counterparts, exceptional points associated with symmetry transitions are an inherent feature, as modes spontaneously and non-perturbatively lock their phase to the oscillations of the material. We further investigate the limiting behaviour of the Floquet quasinormal modes in large cavities. Distinct non-perturbative behaviour arises in time-modulated systems as increasingly large time-crystal cavities come closer to achieving the maximum gain predicted from a bulk wavenumber bandgap.

physics.optics↗

arXiv2024

Symmetry-Protected Lossless Modes in Dispersive Time-Varying Media

We give an exact application of a recently developed, operator-based theory of wave propagation in dispersive, time-varying media. Using this theory we find that the usual symmetry of complex conjugation plus changing the sign of the frequency, required for real valued fields, implies that the allowed propagation constants in the medium are either real valued or come in conjugate pairs. The real valued wave numbers are only present in time-varying media, implying that time variation leads to modes that are free from dissipation, even in a lossy medium. Moreover, these symmetry-unbroken waves lack a defined propagation direction. This can lead to a divergent transmission coefficient when waves are incident onto a finite, time-varying slab. The techniques used in this work present a route towards further analytic applications of this operator formalism.

physics.optics↗

arXiv2022

Optimizing achromaticity in metalenses, and development of a layered thin-film metalens

Metalenses are ultrathin optical devices designed to replicate behavior of conventional refractive lenses, or lens arrays, utilizing nanoscale resonant structures to redirect incident light. These are often comprised of discrete meta-atoms such as nanoscale dielectric pillars. Achromatic focusing - associated with traditional multi-element refractive counterparts - is frequently attempted with single-layer metalens designs, which has proven difficult to achieve with bounded refractive indices and total lens thickness. A recent study (F.Presutti and F.Monticone, 2020) formalized this, applying optical delay-line limitations to metalenses, resulting in a generalized trade-off in achromaticity for focusing systems. In this work, we (1) theoretically explore achromaticity in metalens design, and (2) propose a thin-film multilayer design as an alternative to the discrete meta-atom approach for large numerical aperture (NA) achromatic metalenses. It is shown that wavefront modulation can also be achieved with spectrally-varying transmission magnitudes, rather than purely matching a phase profile. In fact, even with a bounded refractive index, perfect achromatic operation over a given spectral range can be offset by imperfect operation elsewhere, resulting in a NA limited by the smallest general spectral feature controlled. These considerations lead to a generalized phase-matching optimization routine, and a thin-film metalens is simulated, utilizing layered TiO2/MgF2 with total thicknesses under 1 μm (20 layers), focusing across 6 simultaneous wavelengths (350-740 nm, Δλ~65 nm). A significant proportion (>40% spectral average) of the reflected light is focused for moderate NA (~0.35). With the maturity of the optical coating industry, the conformal thin-film approach reduces manufacturing complexity from its discrete nanoscale meta-atom equivalents.

physics.optics↗