Grégoire Saerens

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Saerens

First Name

Grégoire

ORCID

0000-0001-8568-8462

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Publications 1 - 10 of 34

Switchable unidirectional second-harmonic emission through GaAs nanoantennas
Xu, Lei; Saerens, Grégoire; Timofeeva, Maria; et al. (2019)
Proceedings of SPIE ~ AOS Australian Conference on Optical Fibre Technology (ACOFT) and Australian Conference on Optics, Lasers, and Spectroscopy (ACOLS) 2019
Solution-derived Barium Titanate as a Platform for Nonlinear Photonic Devices
Talts, Ülle-Linda; Weigand, Helena; Henrique, Franciele; et al. (2024)
3rd Colloquium on the Physics and Applications of Metasurfaces. Abstracts
Image-based autofocusing system for nonlinear optical microscopy with broad spectral tuning
Saerens, Grégoire; Lang, Lukas; Renaut, Claude; et al. (2019)
Optics Express
We present an image-based autofocusing system applied in nonlinear microscopy and spectroscopy with a wide range of excitation wavelengths. The core of the developed autofocusing system consists of an adapted two-step procedure maximizing an image score with six different image scorings algorithms implemented to cover different types of focusing scenarios in automated regime for broad wavelength region. The developed approach is combined with an automated multi-axis alignment procedure. We demonstrate the key abilities of the autofocusing procedure on different types of structures: single nanoparticles, nanowires and complex 3D nanostructures. Based on these experiments, we determine the optimal autofocusing algorithms for different types of structures and applications.
Polarization Dynamics of Solid-State Quantum Emitters
Kumar, Anand; Samaner, Çağlar; Cholsuk, Chanaprom; et al. (2024)
ACS Nano
Quantum emitters in solid-state crystals have recently attracted a great deal of attention due to their simple applicability in optical quantum technologies. The polarization of single photons generated by quantum emitters is one of the key parameters that plays a crucial role in various applications, such as quantum computation, which uses the indistinguishability of photons. However, the degree of single-photon polarization is typically quantified using the time-averaged photoluminescence intensity of single emitters, which provides limited information about the dipole properties in solids. In this work, we use single defects in hexagonal boron nitride and nanodiamond as efficient room-temperature single-photon sources to reveal the origin and temporal evolution of the dipole orientation in solid-state quantum emitters. The angles of the excitation and emission dipoles relative to the crystal axes were determined experimentally and then calculated using density functional theory, which resulted in characteristic angles for every specific defect that can be used as an efficient tool for defect identification and understanding their atomic structure. Moreover, the temporal polarization dynamics revealed a strongly modified linear polarization visibility that depends on the excited-state decay time of the individual excitation. This effect can potentially be traced back to the excitation of excess charges in the local crystal environment. Understanding such hidden time-dependent mechanisms can further improve the performance of polarization-sensitive experiments, particularly that for quantum communication with single-photon emitters.
Spontaneous parametric down-conversion in bottom-up grown lithium niobate microcubes
Duong, Ngoc My Hanh; Saerens, Grégoire; Timpu, Flavia; et al. (2022)
Optical Materials Express
Nonclassical light sources are highly sought-after as they are an integral part of quantum communication and quantum computation devices. Typical sources use bulk nonlinear crystals that rely on stringent phase-matching conditions, limiting the operating wavelength and bandwidth. In this work, we demonstrate the generation of photon pairs from a free-standing lithium niobate microcube at the telecommunication wavelength of 1.56 µm through the spontaneous parametric down-conversion process. The maximum photon pair generation rate obtained from a single microcube with the size of 3.6 µm is 490 Hz, resulting in an efficiency of 20.6 GHz/Wm, which is three orders of magnitude larger than the efficiency of biphoton generation in bulk nonlinear crystals. The microcubes are synthesized through a solvothermal method, offering the possibility for scalable devices via bottom-up assembly on any substrates. Our work constitutes an important step forward in the realization of compact nonclassical light sources with a wide bandwidth for various quantum applications.
Ultrafast magnetism: The magneto-optical Kerr effect and conduction electrons
Gort, Rafael; Bühlmann, Kevin; Saerens, Grégoire; et al. (2020)
Applied Physics Letters
Gallium Phosphide Nanowires in a Free-Standing, Flexible, and Semitransparent Membrane for Large-Scale Infrared-to-Visible Light Conversion
Fedorov, Vladimir V.; Bolshakov, Alexey; Sergaeva, Olga; et al. (2020)
ACS Nano
Engineering of nonlinear optical response in nanostructures is one of the key topics in nanophotonics, as it allows for broad frequency conversion at the nanoscale. Nevertheless, the application of the developed designs is limited by either high cost of their manufacturing or low conversion efficiencies. This paper reports on the efficient second-harmonic generation in a free-standing GaP nanowire array encapsulated in a polymer membrane. Light coupling with optical resonances and field confinement in the nanowires together with high nonlinearity of GaP material yield a strong second-harmonic signal and efficient near-infrared (800-1200 nm) to visible upconversion. The fabricated nanowire-based membranes demonstrate high flexibility and semitransparency for the incident infrared radiation, allowing utilizing them for infrared imaging, which can be easily integrated into different optical schemes without disturbing the visualized beam.
From high- to low-contrast: the role of asymmetries in dielectric gratings supporting bound states in the continuum
Vincenti, Maria Antonietta; Carletti, Luca; de Ceglia, Domenico; et al. (2024)
Optics Express
One-dimensional sub-wavelength gratings are versatile photonic platforms supporting diverse resonances, including symmetry-protected bound states in the continuum. However, practical access to these bound modes relies on their quasi-bound form, which necessitates the introduction of perturbations in either geometry or material properties. Despite having a large, finite quality factor, quasi-bound modes retain their characteristically strong field confinement. Gaining control over field localization and leakage of quasi-bound modes requires an investigation not limited to studying the degree of asymmetry and the incoming polarization. Here, we demonstrate that by carefully combining specific types of asymmetries and refractive index contrast between the grating and its surrounding environment, one can tailor field localization and Q-factor almost at will. Our findings reveal a strategic roadmap for optimizing quasi-bound mode implementation, dramatically improving their use in applications such as optical communication, sensing, and nonlinear optical processes.
Role of asymmetries in q-BIC formation
Weigand, Helena; Millet, Loïc; Carletti, Luca; et al. (2024)
Proceedings of SPIE ~ Metamaterials XIV
Bound states in the continuum can be defined as non-radiating resonant modes within open environments. These modes share a defining characteristic of being dark, displaying an exceptional degree of field localization. However, their practical accessibility lies in their quasi-bound form, which needs the introduction of perturbations in the system's geometry or material properties. Despite a finite, albeit high, quality factor, the quasi-bound modes manage to retain their characteristic strong field localization. In this presentation, our focus will be directed towards the exploration of symmetry-protected bound states in the continuum, delving into a comprehensive analysis of the impact that the introduction of various types of asymmetries can have on the formation and behavior of their quasi-bound counterparts. In particular, we will focus our attention on metasurfaces made of BaTiO3, whose constituent elements are periodically arranged nanowires. By investigating the topological features that contribute to certain mode selection rules, our analysis aims to provide a deeper understanding of the underlying mechanisms governing the formation and behavior of these modes. Our findings provide a strategic roadmap for optimizing the implementation of quasi-bound modes and provide a clear path to exploit them in specific applications such as sensing and nonlinear optical processes.
Switching Second-Harmonic Forward to Backward Emission via GaAs Nanoantennas
Xu, Lei; Saerens, Grégoire; Timofeeva, Maria; et al. (2020)
OSA Technical Digest ~ Conference on Lasers and Electro-Optics
Switching forward-to-backward linear scattering of nanoantennas is a process of major importance. Here, we demonstrate the first nonlinear switching of forward to backward second harmonic generation, via engineering the nonlinear-tensors of the (110)-GaAs nanoantennas.

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Grégoire Saerens

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