arXiv subjects

Virginie Brändli

Publications and source records attributed to Virginie Brändli.

4 recordsLinked to original sources

arXiv2026

Unveiling nanolaser physics: Non-Perturbative Measurement of the Lasing-Mode Photon Population at the Sub-Picoseconds and Nanometer Scale

Semiconducting nanowire lasers (NWLs) constitute nanometer-scale modular and tunable light sources hence an essential component for integrated opto-electronics. However, improving and optimizing NWL operation requires characterization of their near-field and dynamics at the nanometer scale, which is hampered by the light diffraction limit. In this article, we show how to non-perturbatively measure the absolute number of photons in the nanolaser cavity above the lasing threshold with sub-picosecond resolution using a GaN nanowire nanolaser, as well as map the lasing mode spatial profile at the nanoscale. This technique, based on the simultaneous measurements of the photon induced near-field electron microscopy (PINEM) and the photons far-field, allows for the complete nanoscale and time-resolved characterization of a NWL in operation while monitoring its macroscopic optical properties.

physics.optics↗

arXiv2026

Localized emission in MoSe$_2$ monolayers on GaN nanopillars

Solid-state quantum emitters (QEs) in two-dimensional semiconductors offer compact, chip-compatible sources for quantum photonics. In transition-metal dichalcogenides (TMDs), nanopillars are widely used to induce localized emission, yet the underlying confinement mechanism and the relative roles of strain versus dielectric environment remain unclear. The general problem addressed here is whether strain alone explains quantum emitter formation and placement in MoSe$_2$, or whether dielectric contrast at suspended-supported interfaces is also required. Here, we combine hyperspectral superlocalization of photoluminescence with co-registered AFM topography and phase to map the positions of localized states (LS) in MoSe$_2$ suspended on GaN pillars and correlate them with bending strain and the local dielectric context. Contrary to the common assumption of purely strain-driven activation, LS frequently occur at suspended--supported interfaces around the pillar apex and span a broad strain range without a clear threshold, while being scarce along high-strain ripples. Our data indicate that deterministic emitter positioning in Mo-based TMDs benefits from co-engineering both strain gradients and nanoscale dielectric heterogeneity, rather than strain alone. More broadly, this combined optical-mechanical characterization approach provides a general framework for mapping structure-property relationships in 2D quantum materials at the single-emitter level.

cond-mat.mes-hall↗

arXiv2025

Diffraction-limited operation of micro-metalenses: fundamental bounds and designed rules for pixel integration

Metasurfaces provide a compact, flexible, and reliable solution for controlling the wavefront of light. In imaging systems, micro-lens arrays are integrated with pixel matrices to reduce optical crosstalk, enhance photon collection efficiency, and improve spatial resolution. However, as the aperture size of the photonic devices decreases, fundamental limitations associated with diffraction emerge. Here, we theoretically analyze and experimentally demonstrate that these constraints also affect the performance of small functionalized apertures, including metasurfaces and metalenses, emphasizing the increasing impact of diffraction at small pixel sizes. Despite their design versatility, our findings reveal the necessity of accounting for fundamental diffraction properties to optimize the performance of miniature optical metasurfaces.

physics.optics↗

arXiv2020

Analysis of low-threshold optically pumped III-nitride microdisk lasers

Low-threshold lasing under pulsed optical pumping is demonstrated at room temperature for III-nitride microdisks with InGaN/GaN quantum wells on Si in the blue spectral range. Thresholds in the range of 18 kW/cm2 have been achieved along with narrow linewidths of 0.07 nm and a large peak to background dynamic of 300. We compare this threshold range with the one that can be calculated using a rate equation model. We show that thresholds in the few kW/cm2 range constitute the best that can be achieved with III-nitride quantum wells at room temperature. The sensitivity of lasing on the fabrication process is also discussed.

physics.app-ph↗