arXiv subjects

Daniel Repp

Publications and source records attributed to Daniel Repp.

6 recordsLinked to original sources

arXiv2026

Optimized near-field optical response via adaptive tip illumination

The performance of tip-enhanced optical microscopy is often limited by inefficient coupling of the excitation field to the plasmonic tip apex, as well as by thermal drift and optical aberrations. Here, we demonstrate that adaptive wavefront shaping based on Zernike mode provides a practical approach to achieving robust near-field optimisation at the tip apex. Using a sequential feedback algorithm, initially using the near-field signal, we narrow the illumination point-spread function and suppress sidelobes. This demonstrates that Zernike-mode control can be used for both aberration correction and field engineering. In tip-enhanced Raman measurements of a Janus MoSSe monolayer, conventional near-field optimisation increases the signal intensity by around 1.4 fold. A second optimisation step based directly on the Raman-band intensity yields a further 5 to 15 fold enhancement, depending on the specific tips used. These results establish a systematic, optics-based strategy for optimising tip fields, providing a transferable framework for improving tip-enhanced and related near-field spectroscopies.

physics.optics↗

arXiv2024

Optical characterization of size- and substrate-dependent performance of ultraviolet hybrid plasmonic nanowire lasers

Nanowire-based plasmonic lasers are now established as nano-sources of coherent radiation, appearing as suitable candidates for integration into next-generation nanophotonic circuitry. However, compared to their photonic counterparts, their relatively high losses and large lasing thresholds still pose a burdening constraint on their scalability. In this study, the lasing characteristics of ZnO nanowires on Ag and Al substrates, operating as optically-pumped short-wavelength plasmonic nanolasers, are systematically investigated in combination with the size-dependent performance of the hybrid cavity. A hybrid nanomanipulation-assisted single nanowire optical characterization combined with high-throughput PL spectroscopy enables the correlation of the lasing characteristics to the metal substrate and the nanowire diameter. The results evidence that the coupling between excitons and surface plasmons is closely tied to the relationship between substrate dispersive behavior and nanowire diameter. Such coupling dictates the degree to which the lasing character, be it more plasmonic- or photonic-like, can define the stimulated emission features and, as a result, the device performance.

physics.optics↗

arXiv2022

Tailoring Nanowire Lasing Modes via Coupling to Metal Gratings

Tailoring the emission of plasmonic nanowire-based lasers represents one of the major challenges in the field of nanoplasmonics, given the envisaged integration of such devices into on-chip all-optical circuits. In this study, we proposed a mode selection scheme based on distributed feedback, achieved via the external coupling of single zinc oxide nanowires to an aluminum grating, which enabled a quasi-single mode lasing action. The nano-manipulation of a single nanowire allowed for a reliable comparison of the lasing emission characteristics in both planar (i.e. nanowire on the metallic substrate) and on-grating configurations. We found that, by varying the orientation of the nanowire on the grating, only when the nano-cavity was perpendicular to the ridge direction, an additional peak emerged in the emission spectrum on the low-energy side of the gain envelope. As a consequence of the fulfillment of the Bragg condition, such a peak was attributed to a hybrid mode dominating the mode competition. Simulation results showed that the hybrid mode could be efficiently waveguided along the nanowire cavity and supported by localized plasmon polaritons building up at the raised features ("fences") on top of the metal grating ridges. Moreover, the hybrid mode was found to experience an extra reflectance of nearly 50% across the grating periods, in addition to that provided by the nanowire end facets.

physics.optics↗

arXiv2022

Lasing modes in ZnO nanowires coupled to planar metals

Semiconductor nanowire lasers can be subject to modifications of their lasing threshold resulting from a variation of their environment. A promising choice is to use metallic substrates to gain access to low-volume Surface-Plasmon-Polariton (SPP) modes. We introduce a simple, yet quantitatively precise model that can serve to describe mode competition in nanowire lasers on metallic substrates. We show that an aluminum substrate can decrease the lasing threshold for ZnO nanowire lasers while for a silver substrate, the threshold increases compared with a dielectric substrate. Generalizing from these findings, we make predictions describing the interaction between planar metals and semiconductor nanowires, which allow to guide future improvements of highly-integrated laser sources.

physics.optics↗

arXiv2020

Laser stabilization to a cryogenic fiber ring resonator

The frequency stability of lasers is limited by thermal noise in state-of-the-art frequency references. Further improvement requires operation at cryogenic temperature. In this context, we investigate a fiber-based ring resonator. Our system exhibits a first-order temperature-insensitive point around $3.55$ K, much lower than that of crystalline silicon. The observed low sensitivity with respect to vibrations ($<5\cdot{10^{-11}}\,\text{m}^{-1} \text{s}^{2}$), temperature ($-22(1)\cdot{10^{-9}}\,\text{K}^{-2}$) and pressure changes ($4.2(2)\cdot{10^{-11}}\,\text{mbar}^{-2}$) makes our approach promising for future precision experiments.

physics.optics↗

arXiv2018

Compact 3D quantum memory

Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit both to a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. The external coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of $6$ with a fidelity of approximately $80\%$ determined via quantum process tomography. We also find that this enhancement is not limited by fundamental constraints.

quant-ph↗