arXiv subjects

Denis Lefebvre

Publications and source records attributed to Denis Lefebvre.

3 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↗

arXiv2024

A negative index metamaterial driven by phonons on a ZnO platform

Negative index metamaterials (NIMs) can be achieved with uniaxial hyperbolic metamaterials (HMMs) featuring $\epsilon_{parallel}>0$ and $\epsilon_{perpendicular}<0$. This type of approach has been traditionally realized using stacked doped/undoped semiconductor layers. Only recently surface phonon polaritons (SPhPs) have emerged as a promising low-loss alternative to surface plasmon polaritons (SPPs). Despite this advantage, the SPhP-based approach has been underexplored due to the challenges associated with ensuring high crystal quality in the heterostructure when using alloys with different phonon frequencies. In this work, we design a phononic-driven NIM using a ZnO/(Zn,Mg)O heterostructure, demonstrating control over its hyperbolic behavior through the precise selection of the Mg content and the relative layer thicknesses. Our study shows that increasing the Mg content in the ternary layers enhances the type I behavior, and that the optimal layer thickness varies depending on the Mg content. After analyzing the conditions for achieving type I hyperbolic dispersion, we experimentally demonstrate this concept with a sample featuring equal layer thicknesses and a 32% Mg concentration. We characterize the structure by means of polarized reflectance spectroscopy and use attenuated total reflectance spectroscopy to report the presence of a SPhP mode located within the type I hyperbolic region. By employing the transfer matrix method, we demonstrate that this mode exhibits negative frequency dispersion, a hallmark of type I hyperbolic modes, and isofrequency curve calculations further confirm this behavior. Controlling the design of a phononic hyperbolic type I metamaterial lays the groundwork for exploring its potential applications in attaining low-loss, sub-diffraction-limited optical modes using SPhP excitations.

physics.optics↗

arXiv2019

In-situ monitoring of room temperature reactions of lanthanides with nitrogen and hydrogen at low pressures

The dissociative chemisorption of molecular nitrogen on clean lanthanide surfaces at ambient temperature and low pressure is explored. In-situ conductance measurements track the conversion from the lanthanide metals to the insulating lanthanide nitrides. A small partial pressure of oxygen ($\sim 10^{-8}$ mbar) is shown to inhibit the nitridation of lanthanides at $10^{-4}$ mbar of N$_2$. The rate of nitridation as a function of nitrogen pressure is measured at low pressure for a series of lanthanide elements, gadolinium, terbium, dysprosium, ytterbium and praseodymium. Exposure of the lanthanide surfaces to both N$_2$ and H$_2$ results in the formation of NH$_3$.

cond-mat.mtrl-sci↗