arXiv subjects

Helmut Hörner

Publications and source records attributed to Helmut Hörner.

5 recordsLinked to original sources

arXiv2026

Massively Degenerate Coherent Perfect Absorption in Gradient-Index Fibers

Coherent perfect absorbers (CPAs) have recently attracted considerable attention due to their ability to enhance light--matter interaction. By exploiting interference, CPAs enable even weakly absorbing materials to achieve complete absorption under appropriate excitation conditions. Generalizing this concept to the simultaneous absorption of arbitrary multimode input states remains challenging, however, since conventional implementations typically operate only for a single or a very small number of input channels. Here, we propose a compact realization of a multimode coherent perfect absorber based on a gradient-index (GRIN) fiber. Using the self-imaging property of the fiber, the bulky free-space architecture of previous approaches is replaced by a monolithic waveguiding platform that supports near-degenerate rephasing of many spatial modes. We show that standard GRIN profiles optimized for minimal intermodal dispersion enable highly efficient absorption of complex multimode fields, with field-of-view reflectivities well below $1\%$ for realistic parameters. This approach provides a practical and scalable route toward efficient multimode absorption in fiber-based and integrated photonic systems, with potential applications in light harvesting, optical control, and imaging.

physics.optics↗

arXiv2025

Properties of quantum emitters in different hBN sample types particularly suited for nanophotonic integration

Single photon emitters in two-dimensional (2D) hexagonal boron nitride (hBN) are promising solid-state quantum emitters for photonic applications and quantum networks. Despite their favorable properties, much is still unknown about their characteristics and their atomic origin. We focus on two different kinds of hBN samples that particularly lend themselves for integration with nanophotonic devices, multilayer nanoflakes produced by liquid phase exfoliation (LPE) and a layer-engineered sample from hBN grown by chemical vapour deposition (CVD). We investigate their inherent defects and fit their emission properties to computationally simulated optical properties of likely carbon-related defects. Thereby we compare and elucidate the properties in different sample types particularly suited for photonic quantum networks and narrow down the origin of emitters found in these samples. Our work is thus an important step towards harnessing the full potential of single photon emitters in hBN.

quant-ph↗

arXiv2024

Coherent Perfect Absorption of Arbitrary Wavefronts at an Exceptional Point

A Coherent Perfect Absorber (CPA) exploits the interferometric nature of light to deposit all of a light field's incident energy into an otherwise weakly absorbing sample. The downside of this concept is that the necessary destructive interference in CPAs gets easily destroyed both by spectrally or spatially detuning the incoming light field. Each of these two limitations has recently been overcome by insights from exceptional-point physics and by using a degenerate cavity, respectively. Here, we show how these two concepts can be combined into a new type of cavity design, which allows broadband exceptional-point absorption of arbitrary wavefronts. We present two possible implementations of such a Massively Degenerate Exceptional-Point absorber and compare analytical results with numerical simulations.

physics.optics↗

arXiv2023

Imaging and Identification of Single Nanoplastic Particles and Agglomerates

Currently the extent of nanoplastic in the environment can only be estimated by extrapolation from the plastic waste that can be detected. To be able to quantify the whole extent of the problem, detection methods have to be developed that can also identify particles that are smaller than 1 $μ$m. Here we employ surface-enhanced Raman scattering (SERS) to image and identify single nanoplastic particles down to 100 nm in size. We obtain an experimental enhancement factor of more than three orders of magnitude measured on a single plastic particle instead of averaging over a concentration. Our results contribute to the better understanding and employment of SERS for nanoparticle detection and present an important step for the development of future sensors.

physics.optics↗

arXiv2022

Massively degenerate coherent perfect absorber for arbitrary wavefronts

One of the key insights in the emerging field of non-Hermitian photonics is that well-established concepts like the laser can be operated in reverse to realize a 'coherent perfect absorber' (CPA). While conceptually appealing, such CPAs are limited so far to a single, judiciously shaped wavefront or 'mode'. Here, we demonstrate how this limitation can be overcome by time-reversing a 'degenerate cavity laser', based on a unique cavity that self-images any incident light-field onto itself. Placing a weak, critically-coupled absorber into this cavity, we demonstrate that any incoming wavefront, even a complex and dynamically-varying speckle pattern, is absorbed with close to perfect efficiency in a massively parallel interference process. Moreover, the coherent nature of multi-mode absorption allows us to tune the degree of absorption over a wide range. These characteristics open-up interesting new possibilities for applications in light-harvesting, energy delivery, light control, and imaging.

physics.optics↗