arXiv subjects

Filip Ligmajer

Publications and source records attributed to Filip Ligmajer.

18 recordsLinked to original sources

arXiv2026

Optically Induced Thermal Runaway in Phase-Change VO2 Nanostructures

While thermal runaway occurs across diverse physical disciplines, its presence in subwavelength phase-change photonics remains unexplored because existing thermo-optical models break down near sharp optical transitions. Here, we introduce an iterative multiphysics framework coupling full-wave electrodynamics with heat transfer, and we discover optically induced thermal runaway in vanadium dioxide (VO2) nanostructures. The runaway switching threshold depends on the illumination wavelength, ambient temperature, and underlying substrate, with external thermal biasing significantly reducing the optical intensity required for runaway ignition. Our results push forward the modeling of sharp photothermal transitions and provide essential design principles for active metasurfaces, neuromorphic photonic devices, and nanoscale thermal management.

physics.optics↗

arXiv2026

Additive and Subtractive Color Filters Based on Birefringent Dielectric Metasurfaces

Dielectric metasurfaces offer a path to high-efficiency optical components at the sub-wavelength scale. In this work, we utilize the wavelength-dependent birefringence of TiO2 nanopillars to create transmissive color filters with switchable spectral responses. We demonstrate that the same physical nanostructure array can function as either an additive (band-pass) or a subtractive (band-stop) filter solely by rotating an external polarizer. The metasurface was fabricated via a modified damascene process, enabling high-aspect-ratio structures with spatial resolutions down to 250 nm. The filters achieve transmission efficiencies of 70% tailorable across the entire visible spectrum, avoiding the ohmic losses typical of plasmonic alternatives. This approach provides a tunable, high-efficiency platform offering a versatile and compact solution for next-generation high-resolution imaging systems.

physics.optics↗

arXiv2026

Inverse designed full-Stokes polarimetric metasurface with simultaneous wavefront sensing for visible light

Metasurfaces have emerged as a powerful platform for compact optical sensors by replacing bulky lenses with flat arrays of subwavelength nanostructures. In precision optical metrology, the simultaneous mapping of a beam's polarization state and wavefront is crucial for real-time diagnostics of stress-induced birefringence and surface flatness. To achieve this in a compact footprint, existing metasurfaces typically partition their aperture into discrete zones, which inherently restricts the light-gathering efficiency and numerical aperture of the system. Here we demonstrate an inverse-designed metasurface that integrates full-Stokes polarimetry and Shack-Hartmann wavefront sensing within a single, continuous aperture in the visible spectrum. By leveraging an adjoint optimization approach to independently control the geometry and rotation of each nanostructure, we break the aperture-sharing paradigm and utilize the entire pixel area for all channels. When coupled with a shallow neural network to automate peak identification and correct for hardware non-idealities, our device yields a mean polarization reconstruction error of only 0.046 across 100 test states on the Poincar\'e sphere, while simultaneously maintaining the precise focal-spot tracking required for sensitive wavefront tilt detection. This work highlights the capacity of inverse design to generate multifunctional, non-intuitive flat optics that outperforms its traditional counterparts.

physics.optics↗

arXiv2026

Controlled dewetting and phase transition hysteresis of VO2 nanostructures

As artificial intelligence continues to grow, so does the need for more efficient ways to process data. Besides moving from electronic to photonic circuits, a promising approach is to integrate phase-change materials. Vanadium dioxide (VO$_2$) exhibits an ultrafast, near-room-temperature phase transition, characterized by hysteresis and large optical modulation -- making it a promising candidate for short-term memories and for mimicking neural behavior in brain-like computing systems. While the hysteresis behavior of VO$_2$ has been well studied in thin films and nanostructures, practical control and device integration have been limited only to thin films. Here, we demonstrate control over the phase transitions of VO$_2$ nanocylinders via lithographic patterning, controlled crystallization, and controlled dewetting. Because nanostructures are easier to address and consume less power than films, the ability to fabricate them with tailored geometry and hysteresis properties directly on integrated platforms is a key step toward scalable, energy-efficient memory and neuromorphic photonic devices.

cond-mat.mes-hall↗

arXiv2025

Establishing a library of metasurface building blocks through coherence-controlled holographic microscopy

Digital holographic microscopy is a powerful tool for characterizing transparent and reflective phase objects. Its ability to reconstruct amplitude and phase can also offer great insight into wavefront shaping and design of all-dielectric optical metasurfaces. While metasurfaces have reached widespread popularity, their design is often based purely on the results of numerical simulations which can overlook many of the real-world fabrication imperfections. Being able to verify the real phase response of a fabricated device is of great utility for high-performance devices. Here, we use holographic microscopy to validate metalibraries of rectangular TiO2 and Si building blocks. Illumination effects are studied for wavelengths from 600 to 740 nm and linear polarization rotating within the full range of unique states (0 to 180deg). Finally, by varying the numerical aperture of the condenser lens from 0.05 to 0.5 we also study the effects of an off-axis illumination. Comparing the experimental results with simulations from finite-difference time-domain and rigorous coupled-wave analysis, we highlight the limitations of these theoretical predictions and underscore the utility of an experimentally established library of building blocks. We demonstrate that our proposed method of holographic microscopy is both practical and effective for creating a metalibrary that accounts for all fabrication and material imperfections, which is crucial for designing high-efficiency metasurfaces.

physics.optics↗

arXiv2024

Coexisting phases of individual VO$_2$ nanoparticles for multilevel nanoscale memory

Vanadium dioxide (VO$_2$) has received significant interest in the context of nanophotonic metamaterials and memories owing to its reversible insulator-metal transition associated with significant changes in its optical and electronic properties. While the VO$_2$ transition has been extensively studied for several decades, the hysteresis dynamics of individual single-crystal VO$_2$ nanoparticles (NPs) remains largely unexplored. Here, employing transmission electron microscopy techniques, we investigate phase transitions of single VO$_2$ NPs in real time. Our analysis reveals the statistical distribution of the transition temperature and steepness and how they differ during forward (heating) and backward (cooling) transitions. We assess the stability of coexisting phases in individual NPs and prove the persistent multilevel memory at near-room temperatures using only a few VO$_2$ NPs. Our findings shed new light on the underlying physical mechanisms governing the hysteresis of VO$_2$ and establish VO$_2$ NPs as a promising component of optoelectronic and memory devices with enhanced functionalities.

cond-mat.mes-hall↗

arXiv2024

Efficient nanoscale imaging of solid-state phase transitions by transmission electron microscopy demonstrated on vanadium dioxide nanoparticles

We present annular dark field scanning transmission electron microscopy (ADF-STEM) as an efficient, fast, and non-destructive nanoscale tool for monitoring solid-state phase transition. Using metal-insulator transition in vanadium dioxide nanoparticles as an example, we characterize lattice and electronic signatures of the phase transition using analytical transmission electron microscopy including diffraction and electron energy-loss spectroscopy. We demonstrate that ADF-STEM shows a clear contrast across the transition, interpreted with the help of convergent electron beam diffraction as stemming from the crystal-lattice modification accompanying the transition. In addition, ADF-STEM utilizes 3--6 orders of magnitude lower electron dose when compared to electron microscopy techniques able to reveal the phase transition with the same spatial resolution and universality. The benefits of ADF-STEM are emphasized by recording a full hysteresis loop for the metal-insulator transition of a single vanadium dioxide nanoparticle. Our study opens the prospect for fast, non-destructive, large-area and nanoscale characterization of solid-state phase transitions.

cond-mat.mtrl-sci↗

arXiv2023

Active Loss Engineering in Vanadium Dioxide Based BIC Metasurfaces

Metasurfaces have unlocked significant advancements across photonics, yet their efficient active control remains challenging. The active materials required often lack continuous tunability, exhibit inadequate refractive index (RI) changes, or suffer from high losses. These aspects pose an inherent limitation for resonance-shifting based switching: when RI changes are small, the resulting shift is also minor. Conversely, high RI changes typically come with high intrinsic losses necessitating broad modes because narrow ones cannot tolerate such losses. Therefore, larger spectral shifts are required to effectively detune the modes. This paper introduces a novel active metasurface approach that converts the constraint of high intrinsic losses into a beneficial feature. This is achieved by controlling the losses in a hybrid vanadium dioxide (VO$_{2}$) - silicon metasurface, supporting symmetry-protected bound states in the continuum (BICs) within the infrared spectrum. By leveraging the temperature-controlled losses in VO$_{2}$ and combining them with the inherent far-field-coupling tunability of BICs, we gain unprecedented precision in independently controlling both the radiative and nonradiative losses of the resonant system. Our dual-control mechanism allows us to optimize our metasurfaces and we experimentally demonstrate quality factors above 200, a maximum reflectance amplitude of 90%, a relative switching contrast of 78%, and continuous tuning from under- to over-coupling within the infrared spectral range. This study provides a foundation for experimentally and technologically simple, fine-tunable, active metasurfaces for applications ranging from molecular sensors to filters and optical modulators.

physics.optics↗

arXiv2023

Structural color filters with compensated angle-dependent shifts

Structural color filters use nano-sized elements to selectively transmit incident light, offering a scalable, economical and environmentally friendly alternative to traditional pigment- and dye-based color filters. However, their structural nature makes their optical response prone to spectral shifts whenever the angle of incidence varies. We address this issue by introducing a conformal VO2 layer onto bare aluminum structural color filters. The insulator-metal transition of VO2 compensated the spectral shift of the filter's transmission at a 15{\deg} tilt with 80% efficiency. Unlike solutions that require adjustment of the filter's geometry, this method is versatile and suitable also for existing structural filters. Our findings also establish tunable materials in general as a possible solution for angle-dependent spectral shifts.

physics.optics↗

arXiv2023

Chiral nanoparticle chains on inorganic nanotube templates

Fabrication of chiral assemblies of plasmonic nanoparticles is a highly attractive and challenging task with promising applications in light emission, detection, and sensing. So far, primarily organic chiral templates have been used for chirality inscription. However, this significantly limits the variety of nanoparticle preparation techniques to an in-pot approach at very low synthesis temperatures. Here, we demonstrate utilization of seemingly achiral inorganic nanotubes as templates for the chiral assembly of nanoparticles. We show that both metallic and dielectric nanoparticles can be attached to scroll-like chiral edges propagating on the surfaces of WS2 nanotubes. Due to relatively high temperature stability of these nanotubes, such assembly can be performed at temperatures as high as 550 {\deg}C. This large temperature range significantly widens the portfolio of usable nanoparticle fabrication techniques, allowing us to demonstrate a variety of chiral nanoparticle assemblies, ranging from metals (Au, Ga) and semiconductors (Ge) to oxides (WO3).

cond-mat.mtrl-sci↗

arXiv2023

Phase-resolved optical characterization of nanoscale spin waves

We study theoretically and experimentally the process of Brillouin light scattering on an array of silicon disks on a thin Permalloy layer. We show that phase-resolved Brillouin light scattering microscopy performed on an array of weakly interacting dielectric nanoresonators can detect nanoscale waves and measure their dispersion. In our experiment, we were able to map the evolution of the phase of the spin wave with a wavelength of 209 nm with a precision of 6 nm. These results demonstrate the feasibility of all-optical phase-resolved characterization of nanoscale spin waves.

physics.optics↗

arXiv2022

Pulsed laser deposition of Sb2S3 films for phase-change tunable nanophotonics

Non-volatile phase-change materials with large optical contrast are essential for future tunable nanophotonics. Antimony trisulfide (Sb2S3) has recently gained popularity in this field due to its low absorption in the visible spectral region. Although several Sb2S3 deposition techniques have been reported in the literature, none of them was optimized with respect to the lowest possible absorption and largest optical contrast upon the phase change. Here, we present a comprehensive multi-parameter optimization of pulsed laser deposition of Sb2S3 towards this end. We correlate the specific deposition and annealing parameters with the resulting optical properties and propose the combination leading to films with extraordinary qualities ({\Delta}n = 1.2 at 633 nm). Finally, we identify crystal orientations and vibrational modes associated with the largest change in the refractive index and propose them as useful indicators of the Sb2S3 switching contrast.

physics.optics↗

arXiv2022

Observing high-k magnons with Mie-resonance-enhanced Brillouin light scattering

Magnonics is a prospective beyond CMOS technology which uses magnons, the quanta of spin waves, for low-power information processing. Many magnonic concepts and devices were recently demonstrated at macro- and microscale, and now these concepts need to be realized at nanoscale. Brillouin light scattering spectroscopy and microscopy (BLS) has become a standard technique for spin wave visualization and characterization, and enabled many pioneering magnonic experiments. However, due to its fundamental limit in maximum detectable magnon momentum, the conventional BLS cannot be used to detect nanoscale spin waves. Here we show that optically induced Mie resonances in dielectric nanoparticles can be used to extend the range of accessible spin wave wavevectors beyond the BLS fundamental limit. The method is universal and can be used in many magnonic experiments dealing with thermally excited as well as coherently excited high-momentum, short-wavelength spin waves. This discovery significantly extends the usability and relevance of the BLS technique for nanoscale magnonic research.

cond-mat.mes-hall↗

arXiv2021

Optically tunable Mie-resonance VO2 nanoantennas for metasurfaces in the visible

Metasurfaces are ultrathin nanostructured surfaces that can allow arbitrary manipulation of light. Implementing dynamic tunability into their design could allow the optical functions of metasurfaces to be rapidly modified at will. The most pronounced and robust tunability of optical properties is provided by phase-change materials such as vanadium dioxide (VO2) and germanium antimony telluride (GST), but their implementations have been limited only to near-infrared wavelengths. Here, we demonstrate that VO2 nanoantennas with widely tunable Mie resonances can be utilized for designing tunable metasurfaces in the visible range. In contrast to the dielectric-metallic phase transition-induced tunability in previous demonstrations, we show that dielectric Mie resonances in VO2 nanoantennas offer remarkable scattering and extinction modulation depths (5-8 dB and 1-3 dB, respectively) for tunability in the visible. Moreover, these strong resonances are optically switchable using a continuous-wave laser. Our results establish VO2 nanostructures as low-loss building blocks of optically tunable metasurfaces.

physics.optics↗

arXiv2020

Single-Shot Orientation Imaging of Nanorods Using Spin-to-Orbital Angular Momentum Conversion of Light

The key information about any nanoscale system are orientations and conformations of its parts. Unfortunately, these details are often hidden below the diffraction limit and elaborate techniques must be used to optically probe them. Here, we present a single-shot imaging technique allowing time-resolved monitoring of rotation motion of metal nanorods, realized in a wide-field regime and with no ambiguity of the measured angles. In our novel method, the nanorod orientation is imprinted onto a geometric phase of scattered light composed of the opposite spin states. By spin-to-orbital angular momentum conversion, we generate two oppositely winding helical waves (optical vortices) that are used for restoring the nanorod in-plane orientation. The method was calibrated using lithographically fabricated nanorods and tested by the rotation imaging of immobilized and moving sub-100 nm colloidal nanorods (measurement accuracy of 2.5{\deg}). We envision this technique can be used also for estimation of nanorod aspect ratios and their out-of-plane orientations.

physics.optics↗

arXiv2019

Silver Amalgam Nanoparticles and Microparticles: A Novel Plasmonic Platform for Spectroelectrochemistry

Plasmonic nanoparticles from unconventional materials can improve or even bring some novel functionalities into the disciplines inherently related to plasmonics such as photochemistry or (spectro)electrochemistry. They can, for example, catalyze various chemical reactions or act as nanoelectrodes and optical transducers in various applications. Silver amalgam is the perfect example of such an unconventional plasmonic material, albeit it is well-known in the field of electrochemistry for its wide cathodic potential window and strong adsorption affinity of biomolecules to its surface. In this study, we investigate in detail the optical properties of nanoparticles and microparticles made from silver amalgam and correlate their plasmonic resonances with their morphology. We use optical spectroscopy techniques on the ensemble level and electron energy loss spectroscopy on the single-particle level to demonstrate the extremely wide spectral range covered by the silver amalgam localized plasmonic resonances, ranging from ultraviolet all the way to the mid-infrared wavelengths. Our results establish silver amalgam as a suitable material for introduction of plasmonic functionalities into photochemical and spectroelectrochemical systems, where the plasmonic enhancement of electromagnetic fields and light emission processes could synergistically meet with the superior electrochemical characteristics of mercury.

physics.optics↗

arXiv2019

Independent engineering of individual plasmon modes in plasmonic dimers with conductive and capacitive coupling

We revisit plasmonic modes in nanoparticle dimers with conductive or insulating junction resulting in conductive or capacitive coupling. In our study which combines electron energy loss spectroscopy, optical spectroscopy, and numerical simulations, we show coexistence of strongly and weakly hybridized modes. While the properties of the former ones strongly depend on the nature of the junction, the properties of the latter ones are nearly unaffected. This opens up a prospect for independent engineering of different plasmonic modes in a single plasmonic antenna. In addition, we show that Babinet's principle allows to engineer the near field of plasmonic modes independent of their energy. Finally, we demonstrate that combined electron energy loss imaging of a plasmonic antenna and its Babinet-complementary counterpart allows to reconstruct the distribution of both electric and magnetic near fields of localised plasmonic resonances supported by the antenna as well as charge and current antinodes of related charge oscillations.

physics.app-ph↗

arXiv2018

Geometric-phase microscopy for high-resolution quantitative phase imaging of plasmonic metasurfaces with sensitivity down to a single nanoantenna

Optical metasurfaces have emerged as a new generation of building blocks for multi-functional optics. Design and realization of metasurface elements place ever-increasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (non-scanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge. Here, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved by taking full advantage of the polarization selective control of light through the geometric (Pancharatnam-Berry) phase. The measurement is carried out in an inherently stable common-path setup composed of a standard optical microscope and an add-on imaging module. Phase information is acquired from the mutual coherence function attainable in records created in broadband spatially incoherent light by the self-interference of scattered and leakage light coming from the metasurface. In calibration measurements, the phase was mapped with the precision and spatial background noise better than 0.01 rad and 0.05 rad, respectively. The imaging excels at the high spatial resolution that was demonstrated experimentally by the precise amplitude and phase restoration of vortex metalenses and a metasurface grating with 833 lines/mm. Thanks to superior light sensitivity of the method, we demonstrated, for the first time to our knowledge, the widefield measurement of the phase altered by a single nanoantenna, while maintaining the precision well below 0.15 rad.

physics.optics↗