arXiv subjects

Markus Nyman

Publications and source records attributed to Markus Nyman.

7 recordsLinked to original sources

arXiv2026

Broken-symmetry phenomena enhanced by quasi-bound states in the continuum

Many of the most powerful and elegant models in physics are grounded in symmetries. In electrodynamics, for example, geometric symmetries govern the observable effects of light-matter interactions. However, for man-made objects, exact symmetries are rarely met and tiny deviations are common. Nonetheless, even approximate symmetries keep many symmetry-derived rules effectively intact. However, as we will show here, this is not universally true. We demonstrate that an incremental violation of the symmetry of a carefully designed system can produce an optical response maximally different from the unbroken symmetry case. To do so, we exploit symmetry-protected quasi-bound states in the continuum (qBICs). Specifically, we design a four-fold rotationally symmetric metasurface composed of nearly dual-symmetric meta-atoms that supports a pair of spectrally aligned electric and magnetic qBICs. At normal incidence, symmetry forbids helicity-preserving reflection. However, for arbitrarily small deviations from normal incidence, the strong resonant enhancement associated with the qBICs overcomes the near-symmetry suppression and enables perfect helicity-preserving reflection. This rapidly emerging violation of symmetry-rules reveals a fundamental intricacy when it comes to treating near-symmetric systems. At the same time, our work opens the door to novel applications in metrology and sensing.

physics.optics↗

arXiv2025

Resonant states reveal strong light-matter coupling in nanophotonic cavities

Photonic resonances enable control over light-matter interactions, but many key phenomena only emerge in the strong-coupling regime where light and matter excitations fully hybridize. To distinguish between weak and strong coupling, one conventionally studies real-frequency spectra of the hybrid system. However, these spectra only provide indirect estimates of the underlying resonant dynamics, as the resonances reside at complex frequencies. To overcome this contradiction, we demonstrate that photonic resonant states provide a framework for unambiguously distinguishing between weak and strong coupling. Upon tracing the resonant states through the complex plane while changing the resonator geometry, their trajectories undergo a qualitative change at the onset of strong coupling. Instead of passing each other in the complex frequency plane with only perturbative interactions, the resonant states swap positions. Assuming a single dominant photonic resonance, we derive an effective Hamiltonian that captures the interaction with multiple material resonances, including direct access to coupling rates from overlap-integrals. Our analysis reveals that, unlike most coupled-oscillator models commonly employed, hybridization not only introduces off-diagonal coupling but also shifts the bare eigenfrequency of the photonic mode. We apply our approach to planar and spherical silver resonators filled with a molecular material whose properties were extracted from quantum-chemical simulations.

physics.optics↗

arXiv2025

Efficient computation of thermal radiation from biperiodic layered systems using the T-matrix method

Metasurfaces are becoming important tools for the control of thermal radiation. Understanding their functional possibilities on computational grounds requires evaluating the response of the biperiodic layered system for many degrees of freedom, including several radiation directions and polarisations, while varying lattice spacing, thicknesses, and/or materials of homogeneous layers, over a range of frequencies. The diverse set of cases that need to be considered in simulations prompts for efficient numerical tools to handle them. To respond to this need, we present a method for computing the thermal radiation from metasurfaces that combines the directional Kirchhoff law with efficient T-matrix based calculations. We show that such a method can accurately reproduce experimental data from a metasurface made of platinum square plates. Additionally, we predict highly circularly polarised emissivity from a chiral metasurface. When comparing CPU-times, the method outperforms other approaches such as rigorous coupled wave analysis already at the modest number of 61 cases per frequency.

physics.optics↗

arXiv2025

Studying thermal radiation with T-matrices

We introduce a basic formalism for computing thermal radiation by combining Waterman's T-matrix method with an algebraic approach to light-matter interactions. The formalism applies to nano-particles, clusters thereof, and also molecules. In exemplary applications, we explore how a chiral structure can induce an imbalance in the circular polarization of thermal radiation. While the imbalance is rather small for a chiral molecule such as R-BINOL, a much larger imbalance is observed for an optimized silver helix of approximately 200 nm in size. Besides the directional Kirchhoff law used in this article, the formalism is suitable for implementing more nuanced theories, and it provides a straightforward path to the computation of thermal radiation spectra of astronomical objects moving at relativistic speeds with respect to the measurement devices.

physics.optics↗

arXiv2024

A Framework for Formulating Polychromatic Theories of Emission

The emission of energy as electromagnetic radiation is ubiquitous, in particular because objects release thermal energy in the form of photons. Most theories of thermal radiation assume that the thermal emissions originate from a continuum of elementary monochromatic sources, uncorrelated to each other. The universality of thermal radiation motivates the consideration of theories that allow for more general kinds of elementary emissions. In here, we introduce a framework for formulating polychromatic theories of emission in the electromagnetic Hilbert space, whose computational side is based on the transition matrix, or T-matrix. Each photon is emitted as a coherent polychromatic pulse. The spectra of the different emitted pulses are derived using the natural resonance frequencies of the given finite-size object. Each resonance belongs to one of the orthogonal subspaces which decompose the absorption operator according to the symmetries of the object. Energy conservation in the steady-state is ensured by equalizing the absorption and emission of energy at each individual subspace. The framework can accommodate general illuminations, and produce emissions with frequencies that are much suppressed in or even absent from the illumination, resulting in different rates of emission and absorption of photons. This makes the framework suitable for describing other kinds of emissions, such as luminescence, in the Hilbert space.

physics.optics↗

arXiv2024

Polarization-dependent effects in vibrational absorption spectra of 2D finite-size adsorbate islands on dielectric substrates

In the last years, Infrared Reflection-Absorption Spectroscopy (IRRAS) became a standard technique to study vibrational excitations of molecules. These investigations are strongly motivated by perspective applications in monitoring chemical processes. For a better understanding of the adsorption mechanism of molecules on dielectrics, the polarization-dependence of an interaction of infrared light with adsorbates at dielectric surfaces is commonly used. Thus, the peak positions in absorption spectra could be different for s- and p-polarized light. This shift between the peak positions depends on both the molecule itself and the dielectric substrate. While the origin of this shift is well understood for infinite two-dimensional adsorbate layers, finite-size samples, which consist of 2D islands of a small number of molecules, have never been considered. Here, we present a study on polarization-dependent finite-size effects in the optical response of such islands on dielectric substrates. The study uses a multi-scale modeling approach that connects quantum chemistry calculations to Maxwell scattering simulations. We distinguish the optical response of a single molecule, a finite number of molecules, and a two-dimensional adsorbate layer. We analyze CO and CO$_2$ molecules deposited on CeO$_2$ and Al$_2$O$_3$ substrates. The evolution of the shift between the polarization-dependent absorbance peaks is firstly studied for a single molecule, which it does not exhibit for at all, and for finite molecular islands, which it increases with increasing island size for, as well as for an infinite two-dimensional adsorbate layer. In the latter case, the agreement between the obtained results and the experimental IRRAS data and more traditional three/four-layer-model theoretical studies supports the predictive power of the multi-scale approach.

physics.optics↗

arXiv2023

A digital twin for a chiral sensing platform

Nanophotonic concepts can improve many measurement techniques by enhancing and tailoring the light-matter interaction. However, the optical response of devices that implement such techniques can be intricate, depending on the sample under investigation. That combination of a promise and a challenge makes nanophotonics a ripe field for applying the concept of a digital twin: a digital representation of an entire real-world device. In this work, we detail the concept of a digital twin with the example of a nanophotonically-enhanced chiral sensing platform. In that platform, helicity-preserving cavities with diffractive mirrors enhance the light-matter interaction between chiral molecules and circularly polarized light, allowing a faster measurement of the circular dichroism of the molecules. However, the sheer presence of the molecules affects the cavity's functionality, demanding a holistic treatment to understand the device's performance. In our digital twin, optical and quantum chemistry simulations are fused to provide a comprehensive description of the device with the molecules across all length scales and predict the circular dichroism spectrum of the device containing molecules to be sensed. Performing simulations in lockstep with the experiment will allow a clear interpretation of the results of complex measurements. We also demonstrate how to design a cavity-enhanced circular dichroism spectrometer by utilizing our digital twin. The digital twin can be used to guide experiments and analyze results, and its underlying concept can be translated to many other optical experiments.

physics.optics↗