Professor at University of Amsterdam
Recent news
Publications
Ludovica Guarneri; Thomas Bauer; Qitong Li; Jung‐Hwan Song; Skyler P Selvin; Ashley P Saunders; Fang Liu; Mark L Brongersma; Jorik van de Groep
Dynamic Excitonic Beam Switching with Atomically‐Thin Binary Blazed Gratings Journal Article
In: Advanced Optical Materials, vol. 13, iss. 15, pp. 2403257, 2025.
@article{guarneri2025dynamic,
title = {Dynamic Excitonic Beam Switching with Atomically‐Thin Binary Blazed Gratings},
author = {Ludovica Guarneri and Thomas Bauer and Qitong Li and Jung‐Hwan Song and Skyler P Selvin and Ashley P Saunders and Fang Liu and Mark L Brongersma and Jorik van de Groep},
doi = {10.1002/adom.202403257},
year = {2025},
date = {2025-05-12},
urldate = {2025-05-12},
journal = {Advanced Optical Materials},
volume = {13},
issue = {15},
pages = {2403257},
abstract = {Beam steering metasurfaces are ultra-compact optical coatings that offer on-demand redirection of optical power to specific diffraction orders. To achieve this, spatial gradients are commonly introduced in the phase of light scattered by plasmon or Mie resonant nanoparticles within the metasurface grating's unit cell. However, these phase gradients are oftentimes difficult to tune post-fabrication. Recently, excitons in monolayer 2D semiconductors have emerged as a new metasurface building block, due to their strong and electrically-tunable resonant light-matter interaction. These 2D excitonic metasurfaces offer the tantalizing prospect of beam switching within a single monolayer. Here, it is demonstrated how the 2D analog of binary blazed gratings enables such beam switching by mere nanopatterning of a large monolayer WS2, even though nanoscale ribbons of WS2 do not support geometrical resonances. By introducing a gradient in the nanoribbon width within the metasurface unit cell, an amplitude gradient combined with a small phase gradient in the scattered fields results in asymmetric diffraction efficiencies. Using a scattered-field analysis, it is shown that these gradients can be further engineered via interference effects with the substrate reflection. Finally, the electrical tunability of the exciton resonance is leveraged to achieve selective and dynamic beam switching with an atomically-thin metasurface.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Beam steering metasurfaces are ultra-compact optical coatings that offer on-demand redirection of optical power to specific diffraction orders. To achieve this, spatial gradients are commonly introduced in the phase of light scattered by plasmon or Mie resonant nanoparticles within the metasurface grating's unit cell. However, these phase gradients are oftentimes difficult to tune post-fabrication. Recently, excitons in monolayer 2D semiconductors have emerged as a new metasurface building block, due to their strong and electrically-tunable resonant light-matter interaction. These 2D excitonic metasurfaces offer the tantalizing prospect of beam switching within a single monolayer. Here, it is demonstrated how the 2D analog of binary blazed gratings enables such beam switching by mere nanopatterning of a large monolayer WS2, even though nanoscale ribbons of WS2 do not support geometrical resonances. By introducing a gradient in the nanoribbon width within the metasurface unit cell, an amplitude gradient combined with a small phase gradient in the scattered fields results in asymmetric diffraction efficiencies. Using a scattered-field analysis, it is shown that these gradients can be further engineered via interference effects with the substrate reflection. Finally, the electrical tunability of the exciton resonance is leveraged to achieve selective and dynamic beam switching with an atomically-thin metasurface.
Ludovica Guarneri; Qitong Li; Thomas Bauer; Jung-Hwan Song; Ashley P Saunders; Fang Liu; Mark L Brongersma; Jorik van de Groep
Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements Journal Article
In: Nano Letters, 2024.
@article{guarneri2024temperature,
title = {Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements},
author = {Ludovica Guarneri and Qitong Li and Thomas Bauer and Jung-Hwan Song and Ashley P Saunders and Fang Liu and Mark L Brongersma and Jorik van de Groep},
doi = {10.1021/acs.nanolett.4c00694},
year = {2024},
date = {2024-04-05},
journal = {Nano Letters},
abstract = {Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light\textendashmatter interactions due to exciton resonances that enable atomically thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons’ temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton\textendashphonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights into the role of excitonic light scattering in 2D nanophotonic devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light–matter interactions due to exciton resonances that enable atomically thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons’ temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton–phonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights into the role of excitonic light scattering in 2D nanophotonic devices.
Qitong Li; Jung-Hwan Song; Fenghao Xu; Jorik van de Groep; Jiho Hong; Alwin Daus; Yan Joe Lee; Amalya C Johnson; Eric Pop; Fang Liu; Mark L Brongersma
A Purcell-enabled monolayer semiconductor free-space optical modulator Journal Article
In: Nature Photonics, vol. 17, iss. 10, pp. 897-903, 2023.
@article{li2023purcell,
title = {A Purcell-enabled monolayer semiconductor free-space optical modulator},
author = {Qitong Li and Jung-Hwan Song and Fenghao Xu and Jorik van de Groep and Jiho Hong and Alwin Daus and Yan Joe Lee and Amalya C Johnson and Eric Pop and Fang Liu and Mark L Brongersma},
doi = {10.1038/s41566-023-01250-9},
year = {2023},
date = {2023-07-23},
urldate = {2023-07-23},
journal = {Nature Photonics},
volume = {17},
issue = {10},
pages = {897-903},
abstract = {Dephasing and non-radiative decay processes limit the performance of a wide variety of quantum devices at room temperature. Here we illustrate a general pathway to notably reduce the detrimental impact of these undesired effects through photonic design of the device electrodes. Our design facilitates a large Purcell enhancement that speeds up competing, desired radiative decay while also enabling convenient electrical gating and charge injection functions. We demonstrate the concept with a free-space optical modulator based on an atomically thin semiconductor. By engineering the plasmonic response of a nanopatterned silver gate pad, we successfully enhance the radiative decay rate of excitons in a tungsten disulfide monolayer by one order of magnitude to create record-high modulation efficiencies for this class of materials at room temperature. We experimentally observe a 10% reflectance change as well as 3 dB signal modulation, corresponding to a 20-fold enhancement compared with modulation using a suspended monolayer in vacuum. We also illustrate how dynamic control of light fields can be achieved with designer surface patterns. This research highlights the benefits of applying radiative decay engineering as a powerful tool in creating high-performance devices that complements substantial efforts to improve the quality of materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Dephasing and non-radiative decay processes limit the performance of a wide variety of quantum devices at room temperature. Here we illustrate a general pathway to notably reduce the detrimental impact of these undesired effects through photonic design of the device electrodes. Our design facilitates a large Purcell enhancement that speeds up competing, desired radiative decay while also enabling convenient electrical gating and charge injection functions. We demonstrate the concept with a free-space optical modulator based on an atomically thin semiconductor. By engineering the plasmonic response of a nanopatterned silver gate pad, we successfully enhance the radiative decay rate of excitons in a tungsten disulfide monolayer by one order of magnitude to create record-high modulation efficiencies for this class of materials at room temperature. We experimentally observe a 10% reflectance change as well as 3 dB signal modulation, corresponding to a 20-fold enhancement compared with modulation using a suspended monolayer in vacuum. We also illustrate how dynamic control of light fields can be achieved with designer surface patterns. This research highlights the benefits of applying radiative decay engineering as a powerful tool in creating high-performance devices that complements substantial efforts to improve the quality of materials.
Qingyuan Fan; Amr M Shaltout; Jorik van de Groep; Mark L Brongersma; Aaron M Lindenberg
Ultrafast Wavefront Shaping via Space-Time Refraction Journal Article
In: ACS Photonics, vol. 10, iss. 8, pp. 2467-2473, 2023.
@article{fan2023ultrafast,
title = {Ultrafast Wavefront Shaping via Space-Time Refraction},
author = {Qingyuan Fan and Amr M Shaltout and Jorik van de Groep and Mark L Brongersma and Aaron M Lindenberg},
doi = {10.1021/acsphotonics.3c00498},
year = {2023},
date = {2023-07-03},
urldate = {2023-07-03},
journal = {ACS Photonics},
volume = {10},
issue = {8},
pages = {2467-2473},
abstract = {A myriad of metasurfaces have been demonstrated that manipulate light by spatially structuring thin optical layers. Manipulation of the optical properties of such layers in both space and time can unlock new physical phenomena and enable new optical devices. Examples include photon acceleration and frequency conversion, which modifies Snell’s relation to a more general, nonreciprocal form. Here, we combine theory and experiment to realize wavefront shaping and frequency conversion on subpicosecond time-scales by inducing space-time refractive index gradients in epsilon-near-zero (ENZ) films with femtosecond light pulses. We experimentally tune wavefront steering by controlling the incident angle of the beams and the pump\textendashprobe delay without the need for nanostructure fabrication. As a demonstration of this approach, we leverage the ultrafast, high-bandwidth optical response of transparent oxides in their ENZ wavelength range to create large refractive index gradients and new types of nonreciprocal, ultrafast two-dimensional (2D) optics, including an ultrathin transient lens.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A myriad of metasurfaces have been demonstrated that manipulate light by spatially structuring thin optical layers. Manipulation of the optical properties of such layers in both space and time can unlock new physical phenomena and enable new optical devices. Examples include photon acceleration and frequency conversion, which modifies Snell’s relation to a more general, nonreciprocal form. Here, we combine theory and experiment to realize wavefront shaping and frequency conversion on subpicosecond time-scales by inducing space-time refractive index gradients in epsilon-near-zero (ENZ) films with femtosecond light pulses. We experimentally tune wavefront steering by controlling the incident angle of the beams and the pump–probe delay without the need for nanostructure fabrication. As a demonstration of this approach, we leverage the ultrafast, high-bandwidth optical response of transparent oxides in their ENZ wavelength range to create large refractive index gradients and new types of nonreciprocal, ultrafast two-dimensional (2D) optics, including an ultrathin transient lens.
Jorik van de Groep; Qitong Li; Jung-Hwan Song; Pieter G Kik; Mark L Brongersma
Impact of substrates and quantum effects on exciton line shapes of 2D semiconductors at room temperature Journal Article
In: Nanophotonics, iss. 0, 2023.
@article{van2023impact,
title = {Impact of substrates and quantum effects on exciton line shapes of 2D semiconductors at room temperature},
author = {Jorik van de Groep and Qitong Li and Jung-Hwan Song and Pieter G Kik and Mark L Brongersma},
doi = {10.1515/nanoph-2023-0193},
year = {2023},
date = {2023-06-20},
urldate = {2023-06-20},
journal = {Nanophotonics},
issue = {0},
abstract = {Exciton resonances in monolayer transition-metal dichalcogenides (TMDs) provide exceptionally strong light\textendashmatter interaction at room temperature. Their spectral line shape is critical in the design of a myriad of optoelectronic devices, ranging from solar cells to quantum information processing. However, disorder resulting from static inhomogeneities and dynamical fluctuations can significantly impact the line shape. Many recent works experimentally evaluate the optical properties of TMD monolayers placed on a substrate and the line shape is typically linked directly to the material’s quality. Here, we highlight that the interference of the substrate and TMD reflections can strongly influence the line shape. We further show how basic, room-temperature reflection measurements allow investigation of the quantum mechanical exciton dynamics by systematically controlling the substrate reflection with index-matching oils. By removing the substrate contribution with properly chosen oil, we can extract the excitonic decay rates including the quantum mechanical dephasing rate. The results provide valuable guidance for the engineering of exciton line shapes in layered nanophotonic systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Exciton resonances in monolayer transition-metal dichalcogenides (TMDs) provide exceptionally strong light–matter interaction at room temperature. Their spectral line shape is critical in the design of a myriad of optoelectronic devices, ranging from solar cells to quantum information processing. However, disorder resulting from static inhomogeneities and dynamical fluctuations can significantly impact the line shape. Many recent works experimentally evaluate the optical properties of TMD monolayers placed on a substrate and the line shape is typically linked directly to the material’s quality. Here, we highlight that the interference of the substrate and TMD reflections can strongly influence the line shape. We further show how basic, room-temperature reflection measurements allow investigation of the quantum mechanical exciton dynamics by systematically controlling the substrate reflection with index-matching oils. By removing the substrate contribution with properly chosen oil, we can extract the excitonic decay rates including the quantum mechanical dephasing rate. The results provide valuable guidance for the engineering of exciton line shapes in layered nanophotonic systems.
Nayeun Lee; Muyu Xue; Jiho Hong; Jorik van de Groep; Mark L Brongersma
Multi‐resonant Mie Resonator Arrays for Broadband Light Trapping in Ultrathin c‐Si Solar Cells Journal Article
In: Advanced Materials, pp. 2210941, 2023.
@article{lee2023multi,
title = {Multi‐resonant Mie Resonator Arrays for Broadband Light Trapping in Ultrathin c‐Si Solar Cells},
author = {Nayeun Lee and Muyu Xue and Jiho Hong and Jorik van de Groep and Mark L Brongersma},
doi = {10.1002/adma.202210941},
year = {2023},
date = {2023-05-02},
urldate = {2023-05-02},
journal = {Advanced Materials},
pages = {2210941},
abstract = {Effective photon management is critical to realize high power conversion efficiencies for thin crystalline Si (c-Si) solar cells. Standard few-100-µm-thick bulk cells achieve light trapping with macroscopic surface textures covered by thin, continuous antireflection coatings. Such sizeable textures are challenging to implement on ultrathin cells. Here, we illustrate how nanoscale Mie-resonator-arrays with a bi-modal size distribution support multiple resonances that can work in concert to achieve simultaneous antireflection and light-trapping across the broad solar spectrum. We experimentally demonstrate the effectiveness of these light-trapping antireflection coatings (LARCs) on a 2.8-µm-thick c-Si solar cell. The measured short-circuit current and corresponding power conversion efficiency are notably improved, achieving efficiencies as high as 11.2%. Measurements of the saturation current density on completed cells indicate that thermal oxides can effectively limit surface recombination. The presented design principles are applicable to a wide range of solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Effective photon management is critical to realize high power conversion efficiencies for thin crystalline Si (c-Si) solar cells. Standard few-100-µm-thick bulk cells achieve light trapping with macroscopic surface textures covered by thin, continuous antireflection coatings. Such sizeable textures are challenging to implement on ultrathin cells. Here, we illustrate how nanoscale Mie-resonator-arrays with a bi-modal size distribution support multiple resonances that can work in concert to achieve simultaneous antireflection and light-trapping across the broad solar spectrum. We experimentally demonstrate the effectiveness of these light-trapping antireflection coatings (LARCs) on a 2.8-µm-thick c-Si solar cell. The measured short-circuit current and corresponding power conversion efficiency are notably improved, achieving efficiencies as high as 11.2%. Measurements of the saturation current density on completed cells indicate that thermal oxides can effectively limit surface recombination. The presented design principles are applicable to a wide range of solar cells.
