Selected Publications

List of selected publications and theses featuring products made by Vortex Photonics. If you don't see your scientific work in the list or have any other suggestion, please contact us below.

Abstracts are provided for informational purposes only; all copyrights remain with the respective authors and publishers.

2026

Optical Orbital Angular Momentum Detection Using Second-Order Nonlinear Optical Processes
Ju-Young Kim and Minhaeng Cho
ACS Photonics 2026, 13, 4, 1020–1029

View Abstract
Optical vortex beams (OVBs) carrying orbital angular momentum (OAM) offer access to an unbounded set of orthogonal states, enabling a dramatic increase in the information capacity for optical communication systems. However, practical OAM detection in telecommunication platforms remains challenging due to background noise, detector limitations at infrared communication wavelengths, and the destructive nature of conventional sampling methods. Here, we introduce an all-optical, nearly nondestructive OAM detection method based on sum-frequency generation (SFG) that overcomes these limitations by transferring the information on the OAM into a distinct frequency domain. In our scheme, two OVBs─one carrying OAM-encoded information and the other serving as a reference─are coupled within a beta-barium borate (BBO) crystal to generate an SFG signal. Our theoretical and experimental studies demonstrate that SFG efficiency is governed by the spatial overlap of the interacting vortex profiles, providing mode-selective and OAM-resolved detection. Crucially, as only a small fraction of the input photons undergo conversion into the nonlinear signal, the original beams remain functionally intact. Since detection is performed exclusively on the upconverted signal in a spectrally distinct visible wavelength region, the signal-to-noise ratio can be improved. Moreover, the SFG signal is generated only when specific OAM states and temporal overlap conditions are simultaneously satisfied, enabling ultrafast and conditionally gated access to the OAM information. This nonlinear selectivity offers enhanced physical-layer security and high-throughput capabilities. Together, our approach provides a robust and versatile platform for advanced OAM-based optical communications and high-capacity photonics applications.

Twisting harmonics: Transfer of orbital angular momentum in solid-state high-harmonic generation
Debobrata Rajak, Bikash Kumar Das, Rajaram Shrestha, Bálint Kiss, Eric Cormier, Carmelo Rosales-Guzman, Stephan Fritzsche, Qiwen Zhan, Wenlong Gao, Camilo Granados
arXiv:2601.12743v1

View Abstract
Although solid-state platforms underpin modern electronics, little is known about how intense ultrashort light pulses carrying orbital angular momentum (OAM) interact with solids. This gap persists even though, for more conventional light-matter interactions, the complex underlying electron dynamics can often be confined to a single Brillouin zone and described well within the dipole approximation. Previous studies were restricted to nonlinear, perturbative regimes, largely because the generation of intense ultrashort vortex pulses, particularly in the mid-infrared spectral regime, has remained a long-standing challenge. Consequently, the role of structured light in driving nonlinear, non-perturbative processes in solids, and the associated transfer of angular momentum during these interactions, has not been systematically explored. Here, we investigate solid-state high-harmonic generation (HHG) driven by intense ultrashort structured light using a versatile experimental approach applicable to different materials and geometries. We demonstrate that the OAM of the driving field is coherently transferred to the emitted harmonics. In particular, we show that the OAM is conserved independently of the crystal symmetry, the range of electronic interactions, and the presence of strong spin-orbit coupling. These results establish OAM-resolved HHG as a robust framework for characterizing and controlling angular momentum transfer in solid-state HHG and open new avenues for structured-light-driven quantum technologies and topological materials investigations.

Spatially localized optical excitations in a doped solid using robust broadband composite pulses
Niels Joseph, Nikolay V. Vitanov, Thomas Halfmann
Physical Review A 113, 023117 (2026)

View Abstract
We experimentally demonstrate spatial confinement of optically driven atomic excitation by broadband composite pulses in a rare-earth ion-doped crystal. The beam is passed through a spiral phase plate with charge 1 (V-593-20-1, Vortex Photonics), which imprints an azimuthally increasing phase onto the beam, producing a Laguerre-Gaussian mode with a dark central region. The experimental data confirm that broadband composite pulse sequences enable spatially localized excitation well below the diameter of the applied laser beam, with a substantial improvement compared to previous developments and applications of other classes of composite pulses.

2025

Array detection enables large localization range for simple and robust MINFLUX
Eli Slenders, Sanket Patil, Marcus Oliver Held, Alessandro Zunino and Giuseppe Vicidomini
Light: Science & Applications (2025) 14:234

View Abstract
The MINFLUX concept significantly improves the localization properties of single-molecule localization microscopy (SMLM) by overcoming the limit imposed by the fluorophore’s photon counts. Typical MINFLUX microscopes localize the target molecule by scanning a zero-intensity focus around the molecule in a circular trajectory, with smaller trajectory diameters yielding better localization uncertainties for a given number of photons. Since this approach requires the molecule to be within the scanned trajectory, MINFLUX typically relies on an iterative scheme with decreasing trajectory diameters. This iterative approach is prone to misplacements of the trajectory and increases the system’s complexity. In this work, we introduce ISM-FLUX, a novel implementation of MINFLUX using image-scanning microscopy (ISM) with a single-photon avalanche diode array detector. ISM-FLUX provides a precise MINFLUX localization within the trajectory while maintaining a conventional photon-limited uncertainty outside it. The robustness of ISM-FLUX localization results in a larger localization range and greatly simplifies the architecture, which may facilitate broader adoption of MINFLUX.

Open-source sub-nanometer stabilization system for super-resolution fluorescence microscopy
Florencia Edorna, Florencia D. Choque, Giovanni Ferrari, Luciano A. Masullo, Piotr Zdańkowski, Guillermo P. Acuna, Philip Tinnefeld, Alan M. Szalai, Lucía F. Lopez, Andrés Zelcer & Fernando D. Stefani
Light: Science & Applications volume 14, Article number: 385 (2025)

View Abstract
Recent advances in fluorescence nanoscopy have pushed resolution to the 1–10 nm range, enabling the direct visualization of individual molecules even in crowded biological environments. Achieving this level of precision requires rigorous sample drift control. Techniques such as MINFLUX and RASTMIN, which rely on keeping the sample fixed within an excitation pattern, demand active drift correction to achieve their theoretical nanometer-scale resolution limits. Here, we present an active stabilization system for super-resolution microscopy that delivers sub-nm precision for hours. Featuring a simple optical design, the system can be added as a separate module to any fluorescence microscope. We also provide an open-source control software including a user-friendly graphical interface readily adaptable to different setups. We demonstrate the adaptability and performance of the stabilization system with p-MINFLUX and RASTMIN measurements performed in two different setups, reaching the theoretical Cramér-Rao Bound and resolving ~10 nm distances within DNA origami structures.

512-Fold Rotational Super-Resolution via Four-Photon High-Dimensional Structured Light
Guy Tshuva, Ofir Yesharim, Hagai S. Eisenberg, Ady Arie
Laser & Photonics Reviews 2025

View Abstract
Light beams carrying orbital angular momentum (OAM) can be generated in the extreme ultraviolet and soft X-ray spectra by means of high harmonic generation (HHG). In HHG, phase properties of the drive laser, such as curvature, aberrations, and topological charge, are upconverted to the harmonic beams and coherently added to the inherent dipole phase. The strong nonlinearity of the HHG process, combined with the rapid phase variations corresponding to large OAM values in these vortex beams, leads to a high sensitivity to small variations in the driving field. However, a study of the generation dynamics via an accurate reconstruction of multiwavelength OAM beams is challenging. Here we show full complex field measurements of multiple individual harmonics of the HHG vortex beams. By using spectrally resolved ptychographic wavefront sensing, we retrieve the high-resolution amplitude and phase profiles for harmonics 23 to 29 in parallel, enabling detailed multiwavelength beam reconstructions. We study the influence of generation conditions and drive laser aberrations on the resulting vortex fields by comparing measured fields to numerical simulations and retrieving the propagation conditions around the focus and the OAM content of the beams. Specifically, we find that the multimodal content of such vortex beams can significantly influence the propagation and field distributions in the focal region. Such a beam propagation analysis allows a prediction of the resulting attosecond pulse trains and associated attosecond light springs that can be generated under realistic driving conditions.

Generation Dynamics of Broadband Extreme Ultraviolet Vortex Beams
Antonios Pelekanidis, Fengling Zhang, Kjeld S. E. Eikema, Stefan Witte
ACS Photonics 2025, 12, 3, 1638–1649

View Abstract
Light beams carrying orbital angular momentum (OAM) can be generated in the extreme ultraviolet and soft X-ray spectra by means of high harmonic generation (HHG). In HHG, phase properties of the drive laser, such as curvature, aberrations, and topological charge, are upconverted to the harmonic beams and coherently added to the inherent dipole phase. The strong nonlinearity of the HHG process, combined with the rapid phase variations corresponding to large OAM values in these vortex beams, leads to a high sensitivity to small variations in the driving field. However, a study of the generation dynamics via an accurate reconstruction of multiwavelength OAM beams is challenging. Here we show full complex field measurements of multiple individual harmonics of the HHG vortex beams. By using spectrally resolved ptychographic wavefront sensing, we retrieve the high-resolution amplitude and phase profiles for harmonics 23 to 29 in parallel, enabling detailed multiwavelength beam reconstructions. We study the influence of generation conditions and drive laser aberrations on the resulting vortex fields by comparing measured fields to numerical simulations and retrieving the propagation conditions around the focus and the OAM content of the beams. Specifically, we find that the multimodal content of such vortex beams can significantly influence the propagation and field distributions in the focal region. Such a beam propagation analysis allows a prediction of the resulting attosecond pulse trains and associated attosecond light springs that can be generated under realistic driving conditions.

Dynamic Trapping and Printing of Plasmonic Dimers with Optical Vortex Beams
Paul Vosshage, Camila M. Otero, Francis Schuknecht, María Ana Huergo, Jochen Feldmann, Theobald Lohmüller
J. Phys. Chem. C 2025, 129, 17, 8262–8269

View Abstract
In this work, we analyze the motion of gold nanospheres in orbital angular momentum (OAM)-carrying optical vortex traps in real time using darkfield microscopy and high-speed video analysis. Notably, we observe that optical binding between gold nanoparticles within the ring-shaped laser trap leads to increased orbiting speeds at a lower focal plane for gold nanoparticle dimers compared to monomers. This behavior is attributed to stronger optical scattering forces acting on the dimers driven by the emergence of a coupled plasmon mode. As the particles move closer together, this mode red-shifts, becoming more resonant with the laser wavelength, eventually causing the system to transition from optical trapping to optical printing. This finding suggests a general mechanism for one-step dimer printing based on plasmonic coupling in vortex beams by adjusting the laser wavelength or modifying the dielectric environment of the nanoparticles via a molecular coating. The feasibility of this approach is demonstrated for optical printing and subsequent surface-enhanced Raman scattering (SERS) spectroscopy on gold nanoparticle dimers coated with 4-nitrothiophenol.

High-energy generation of arbitrary cylindrical vector vortex beams using a modified Mach–Zehnder interferometer
Justin Harrison, Nokwazi Mphuthi, Chemist Mabena, and Darryl Naidoo
Applied Optics Vol. 64, Issue 9, pp. C60-C68 (2025)

View Abstract
In this paper, we demonstrate the interferometric generation of high-energy pulsed vector vortex beams at arbitrary points on the higher-order Poincaré sphere. Scalar vortex beams with topological charges l=1 and l=2 were produced using fused silica spiral phase plates and a 1064 nm wavelength Gaussian laser source, delivering a pulse energy of 2.75 mJ at a frequency of 1 kHz with a pulse duration of 15.5 ns. A novel, to our knowledge, modified Mach–Zehnder interferometer was constructed to allow for arbitrary inter-modal phase and amplitude control of the vector vortex states across the surface of the Poincaré sphere, achieving pulse energies of 2.5 mJ and peak powers exceeding 160 kW. This marks the highest, to the best of our knowledge, pulse energy achieved for arbitrary higher-order vector vortex beams on the HOPS.

Deep learning-driven adaptive optics for laser wavefront correction
Jikai Wang, Sven Burckhard, Sonam Smitha Ravi, Dominik Bauer, Volker Rominger, Stefan Nolte, and Daniel Flamm
Applied Optics Vol. 64, Issue 29, pp. 8625-8632 (2025)

View Abstract
We report on an intensity-only and deep-learning-based method for laser beam characterization that allows to predict the underlying optical field within milliseconds. A simple near-field/far-field camera setup enables online control of adaptive optics to optimize beam quality. The robustness and precision of the method are enhanced by applying the concept of phase diversity based on spiral phase plates.

Visualization and characterization of arbitrarily shaped pulsed-laser spots
Yann Le-Guen, Maxime Verges, Michel Hehn, Stephane Mangin, and Julius Hohlfeld
Phys. Rev. Applied 23, 044018 – Published 7 April, 2025

View Abstract
A novel way to represent and analyze the contours of laser-pulse-induced domains, which reflect the position at which the laser fluence drops below a certain threshold and are measured as a function of the laser-pulse energy, is introduced. It enables the visualization and quantitative characterization of arbitrarily shaped in situ laser spots with high accuracy.

Extracellular space diffusion modelling identifies distinct functional advantages of archetypical glutamatergic and GABAergic synapse geometries
Paula Gimenez, Rohisha T. Shakya, Fidel Santamaria, Jan Tønnesen
bioRxiv preprint 2025

View Abstract
The brain extracellular space (ECS) is a convoluted compartment of nano- and microscale interconnected ducts. A key step in signaling between neural cells is diffusion of signaling molecules through the ECS, yet, signaling is generally considered solely from the stance of cells and their properties. Where ECS diffusion is addressed, this is commonly done using volume-averaging techniques blind to individual signaling events and ECS geometry. We hypothesized that ECS geometry can shape local diffusion and thereby tune signaling arising from point-sources. To access the scale of individual transmitter release events and synapse geometries, we developed a computational diffusion model, DifFlux, based on super-resolved images of hippocampal ECS in live mouse brain slices and combined this with single molecule Monte Carlo diffusion simulations. Our approach allows us to simulate diffusion of molecules of our choosing in true live ECS geometries. We asked how the ECS shapes local diffusion in dense neuropil and along larger cellular processes in CA1 stratum radiatum. We observed local diffusional anisotropy and directionality imposed by ECS geometry. Further, we identified distinct functional advantages of dendritic spine and somatodendritic synapse ECS geometries, shedding light on the longstanding conundrum of why glutamatergic and GABAergic synapses are so conspicuously morphologically different. Our modelling broadly identifies ECS structure as a direct modulator of extrasynaptic signaling that can operate in parallel to conventional regulation mechanisms.

Sculpting ultrafast mid-infrared light for solid-state high harmonic generation
Camilo Granados, Bálint Kiss, Eric Cormier, Bikash Kumar Das, Debobrata Rajak, Carmelo Rosales-Guzman, Rajaram Shrestha, Qiwen Zhan, Wenlong Gao
arXiv:2512.19412 2025

View Abstract
The ability to sculpt light in space, time, and polarization has revolutionized studies of light-matter interaction and enabled breakthroughs in optical communication, imaging, and ultrafast science. Among the many degrees of freedom of light, orbital angular momentum (OAM) further expands these capabilities by unlocking new regimes of control in information encoding, particle trapping and manipulation, and symmetry-driven selection rules. However, exploiting OAM to drive nonlinear, non-perturbative effects in solids remains challenging, especially in the mid-infrared (MIR) spectral regime-a key region for accessing these effects in ambient air, where spatial light modulators do not operate. Here, we circumvent this limitation by generating femtosecond, few-cycle MIR Bessel-Gauss vortex (BGV) and perfect optical vortices (POVs), using a robust, static spatial-shaping strategy. By utilizing these beams to drive nonlinear optical processes such as second-harmonic generation (SHG) and high-harmonic generation (HHG) in various solid-state materials, we show that the resulting harmonic beams faithfully inherit the structural characteristics of the drivers: the constant-intensity ring of the POVs is preserved across harmonic orders, while the BGV harmonic beams retain their intrinsic topological charge-dependent intensity profiles. Furthermore, by verifying the linear OAM up-scaling law, we confirm the conservation of OAM during SHG and HHG in solids. These results establish strong-field HHG in solids as a robust platform for synthesizing ultrafast structured harmonic light with controllable, high-value OAM.

High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber
Iuliia Zalesskaia, Hassan Asgharzadeh B., Zahra Eslami, Hossein Fathi, Evgenii Gribanov, Andrey Grishchenko, Florian Lindner, Katrin Wondraczek, Evgeny Savelyev, Marco Ornigotti, Valery Filippov, Regina Gumenyuk
arXiv:2512.17645 2025

View Abstract
Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.

Controlling nanomaterial properties with the angular momentum of light
Paula Laborda Lalaguna
PhD thesis, University of Glasgow

View Abstract
The properties of nanomaterials can be tailored through structural and geometrical design, chemical functionalization, strain engineering and other techniques. However,many existing methods for property control are either irreversible or depend on complexphysical set-ups, limiting their practicality and broader technological implementation. This thesis addresses that challenge by developing a non-contact, all-optical approach that leverages the orbital angular momentum carried by Laguerre-Gaussian beams.

The method is investigated for two different applications. In the first instance, the focus is given to orbital angular momentum transfer from Laguerre-Gaussian beams to two dimensional (2D) materials. A theoretical framework for calculating optical forces and torques in dielectric media is presented and angular momentum beams are implemented into a numerical simulation software to predict their effects on the 2D materials. Building on this, a novel, non-contact experimental method is developed to induce wrinkling in two common examples of 2D materials, monolayer graphene and WS2, using the optical torques of Laguerre-Gaussian beams. The out-of-plane deformations and property changes are characterized using various experimental techniques, including electrical conductance measurements, Raman spectroscopy, atomic force microscopy and photoluminescence. The method is reversible and spatially-selective and only limited by sample heterogeneity and monolayer-substrate interactions.

In the second instance, the application of optical angular momentum is extended to chiral sensing. The dynamic control of the optical activity of chiral shuriken meta-materials is demonstrated through numerical simulations and experimental dichroism measurements under varying beam focusing conditions. Together, this thesis highlights the potential of angular momentum beams as a versatile tool for controlling nanomaterial properties with high spatial precision.

2024

MINSTED tracking of single biomolecules
Lukas Scheiderer, Henrik von der Emde, Mira Hesselink, Michael Weber & Stefan W. Hell
Nature Methods volume 21, pages 569–573 (2024)

View Abstract
Here we show that MINSTED localization, a method whereby the position of a fluorophore is identified with precisely controlled beams of a STED microscope, tracks fluorophores and hence labeled biomolecules with nanometer/millisecond spatiotemporal precision. By updating the position for each detected photon, MINSTED recognizes fluorophore steps of 16 nm within <250 μs using about 13 photons. The power of MINSTED tracking is demonstrated by resolving the stepping of the motor protein kinesin-1 walking on microtubules and switching protofilaments.

Breaking Abbe’s diffraction limit with harmonic deactivation microscopy
Kevin Murzyn, Maarten L. S. van der Geest, Leo Guery, Zhonghui Nie, Pieter van Essen, Stefan Witte, and Peter M. Kraus
Science Advances, 13 Nov 2024,Vol 10, Issue 46

View Abstract
Nonlinear optical microscopy provides elegant means for label-free imaging of biological samples and condensed matter systems. The widespread areas of application could even be increased if resolution was improved, which the famous Abbe diffraction limit now restrains. Super-resolution techniques can break the diffraction limit but most rely on fluorescent labeling. This makes them incompatible with (sub)femtosecond temporal resolution and applications that demand the absence of labeling. Here, we introduce harmonic deactivation microscopy (HADES) for breaking the diffraction limit in nonfluorescent samples. By controlling the harmonic generation process on the quantum level with a second donut-shaped pulse, we confine the third-harmonic generation to three times below the original focus size of a scanning microscope. We demonstrate that resolution improvement by deactivation is more efficient for higher harmonic orders and only limited by the maximum applicable deactivation-pulse fluence. This provides a route toward sub-100-nanometer resolution in a regular nonlinear microscope.

Super-resolved FRET and co-tracking in pMINFLUX
Fiona Cole, Jonas Zähringer, Johann Bohlen, Tim Schröder, Florian Steiner, Fernando Stefani and Philip Tinnefeld
Nature Photonics volume 18, pages 478–484 (2024)

View Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) is widely used to investigate dynamic (bio)molecular interactions occurring over distances of up to 10 nm. Recent advances in super-resolution methods have brought their spatiotemporal resolution closer towards the smFRET regime. Although these methods do not suffer from the spatial restrictions of FRET, they only visualize one emitter at a time, thus making it difficult to capture fast dynamics of the interactions. Here we describe two approaches to overcome this limitation in pulsed-interleaved MINFLUX (pMINFLUX) microscopy by using its intrinsic fluorescence lifetime information. First we combine pMINFLUX with smFRET, which enables tracking a FRET donor with nanometre precision while simultaneously determining its distance to a FRET acceptor, yielding the acceptor position by multilateration. Second, we developed pMINFLUX lifetime multiplexing—a method that simultaneously tracks two fluorophores with similar spectral properties but distinct fluorescence lifetimes—to extend co-localized tracking beyond the FRET range. We demonstrate applications on DNA origami systems as well as by imaging the paratopes of an antibody with precision better than 2 nm, paving the way for nanometre precise co-localized tracking for inter-dye distances between 4 nm and 100 nm, and closing the resolution gap between smFRET and co-tracking.

Spatial Control of 2D Nanomaterial Electronic Properties Using Chiral Light Beams
Paula L. Lalaguna, Paul Souchu, Neel Mackinnon, Frances Crimin, Rahul Kumar, Shailendra Kumar Chaubey, Asma Sarguroh, Amy McWilliam, Alexey Y. Ganin, Donald A. MacLaren, Sonja Franke-Arnold, Jörg B. Götte, Stephen M. Barnett, Nikolaj Gadegaard, Malcolm Kadodwala
ACS Nano Vol 18 Issue 31 (2024)

View Abstract
Single-layer two-dimensional (2D) nanomaterials exhibit physical and chemical properties which can be dynamically modulated through out-of-plane deformations. Existing methods rely on intricate micromechanical manipulations (e.g., poking, bending, rumpling), hindering their widespread technological implementation. We address this challenge by proposing an all-optical approach that decouples strain engineering from micromechanical complexities. This method leverages the forces generated by chiral light beams carrying orbital angular momentum (OAM). The inherent sense of twist of these beams enables the exertion of controlled torques on 2D monolayer materials, inducing tailored strain. This approach offers a contactless and dynamically tunable alternative to existing methods. As a proof-of-concept, we demonstrate control over the conductivity of graphene transistors using chiral light beams, showcasing the potential of this approach for manipulating properties in future electronic devices. This optical control mechanism holds promise in enabling the reconfiguration of devices through optically patterned strain. It also allows broader utilization of strain engineering in 2D nanomaterials for advanced functionalities in next-generation optoelectronic devices and sensors.

Wavelength-tolerant generation of Bessel-Gaussian beams using vortex phase plates
Lyubomir Stoyanov, Nikolay Dimitrov, Felix Wiesner, Michael Fedoruk, Gerhard G. Paulus, and Alexander Dreischuh
Applied Optics Vol. 63, Issue 21, pp. 5699-5705 (2024)

View Abstract
With their nearly non-diffracting and self-healing nature, Bessel-Gaussian beams (BGBs) are attractive for many applications ranging from free-space communications to nonlinear optics. BGBs can successfully be generated on background laser beams by imprinting and subsequently annihilating multiply charged optical vortices followed by focusing the resulting ring-shaped beam with a thin lens. For high-power applications optical vortices are preferentially created by spiral phase plates because of their high damage threshold. These are fabricated to realize an azimuthal change of the accumulated phase of a multiple of at a predetermined wavelength. This raises the expectation that the use of spiral phase plates for the generation of BGBs is limited to the design wavelength and therefore not applicable to broadband applications involving short-pulse lasers. In this paper we present experimental data showing that this limitation can be overcome in a broad spectral range around the design wavelength. Experimental cross-sections of the BGBs for several off-design wavelengths are found in a good quantitative agreement with the theoretical Bessel functions at distances up to 540 cm after the focus of the lens.

Quantum enhanced mechanical rotation sensing using wavefront photonic gears
Ofir Yesharim, Guy Tshuva, Ady Arie
APL Photonics 9, 106116 (2024)

View Abstract
Quantum metrology leverages quantum correlations for enhanced parameter estimation. Recently, structured light enabled increased resolution and sensitivity in quantum metrology systems. However, lossy and complex setups impacting photon flux hinder true quantum advantage while using high dimensional structured light. We introduce a straightforward mechanical rotation quantum sensing mechanism, employing high-dimensional structured light and use it with a high-flux (45 000 coincidence counts per second) N00N state source with N = 2. The system utilizes two opposite spiral phase plates with topological charge of up to ℓ = 16 that converts mechanical rotation into wavefront phase shifts and exhibit a 16-fold enhanced super-resolution and 25-fold enhanced sensitivity between different topological charges, while retaining the acquisition times, and with negligible change in coincidence count. Furthermore, the high efficiency together with the high photon flux enables detection of mechanical angular acceleration in real-time. Our approach paves the way for highly sensitive quantum measurements, applicable to various interferometric schemes.

Fourier-transform spectroscopy based on the rotational Doppler effect
Santeri Larnimaa, Markku Vainio
AIP Advances 14, 105329 (2024)

View Abstract
We propose a new Fourier-transform spectroscopy technique based on the rotational Doppler effect. The technique offers an application for optical vortex frequency combs, where each frequency component carries a unique amount of orbital angular momentum (OAM). Here, we emulate a vortex comb using a tunable single frequency laser and a collection of spiral phase plates, generating up to 11 distinct OAM modes. Unlike in traditional Fourier-transform spectroscopy based on the Michelson interferometer (linear Doppler effect), the spectral resolution of vortex-comb spectroscopy is not limited by the mechanical scan distance of the instrument but only by the measurement time. Although the spectrometer requires just one free-running frequency comb, the down-conversion scheme resembles dual-comb spectroscopy, leading to fast mode-resolved measurements.

Illumination diversity in multi-wavelength extreme ultraviolet ptychography
Stefan Witte, Antonios Pelekanidis, Fengling Zhang, Matthias Gouder, Jacob Seifert, Mengqi Du, Kjeld Eikema
Optica Open Preprint (2024)

View Abstract
With the development of high harmonic generation (HHG), lensless extreme-ultraviolet (XUV) imaging at nanoscale resolution has become possible with table-top systems. Specifically, ptychographic phase retrieval using monochromatic XUV illumination exhibits extraordinary robustness and accuracy to computationally reconstruct both the object and the illumination beam profile. In ptychography, using structured illumination has been shown to improve reconstruction robustness and image resolution by enhancing high-spatial-frequency diffraction. However, broadband imaging has remained challenging, as the required multi-wavelength algorithms become increasingly demanding. One major aspect is the ability to separate the available information into different physically meaningful states, such as different spectral components. Here we show that introducing spatial diversity between spectral components of a HHG beam can significantly improve multi-wavelength XUV ptychography. We quantify the diversity in the polychromatic illumination by analyzing the diffraction patterns using established geometry- and information theory-based dissimilarity metrics. We experimentally verify the major influence of diversity by comparing ptychography measurements using HHG beams with Gaussian and binary structured profiles, as well as with beams carrying wavelength-dependent orbital angular momentum. Our results demonstrate how structured illumination acts in a twofold way, by both separating the spectral information in a single diffraction pattern while providing maximized added information with every new scan position. We anticipate our work to be a starting point for high-fidelity polychromatic imaging of next-generation nanostructured devices at XUV and soft-X-ray wavelengths.

Parallel illumination for depletion microscopy through acousto-optic spatial light modulation
Fabian Klingmann, Nick Toledo-García, Estela Martín-Badosa, Mario Montes-Usategui and Jordi Tiana-Alsina
J. Eur. Opt. Society-Rapid Publ., 20 2 (2024) 30

View Abstract
State-of-the-art super-resolution microscopy techniques, including Stimulated Emission Depletion (STED), Reversible Saturable Optical Fluorescence Transitions (RESOLFT), and Switching Laser Mode (SLAM) microscopies, implement Laguerre-Gaussian beams, also known as vortex or doughnut beams to capture fluorescence information within a sub-wavelength area of the observed sample, effectively surpassing the diffraction limit and significantly improving the quality of the image. However, these techniques typically operate at point by point basis, involving time-consuming scanning of the sample to construct a complete, meaningful image. Therefore, for real-time live cell imaging purposes, the parallelization of illumination is crucial. In this study, we demonstrate the parallel generation of arbitrary arrays of Gaussian and Laguerre-Gaussian laser foci suitable for super-resolution microscopy. We achieve rapid scanning through the sample using acousto-optic spatial light modulation, a technique we have previously pioneered across various fields. By employing parallelized illumination with both Gaussian and doughnut beams, we aim to capture super-resolution images.

Array Detection Enables Large Localization Range for Simple and Robust MINFLUX
Eli Slenders, Sanket Patil, Marcus Oliver Held, Alessandro Zunino, Giuseppe Vicidomini
bioRxiv (2024)

View Abstract
The MINFLUX concept significantly enhances the spatial resolution of single-molecule localization microscopy (SMLM) by overcoming the limit imposed by the fluorophore’s photon counts. Typical MINFLUX microscopes localize the target molecule by scanning a zero-intensity focus around the molecule in a circular trajectory, with smaller trajectory diameters yielding lower localization uncertainties for a given number of photons. Since this approach requires the molecule to be within the scanned trajectory, MINFLUX typically relies on a photon-demanding iterative scheme with decreasing trajectory diameters. Although the iterative procedure does not substantially reduce the photon efficiency of MINFLUX, this approach is prone to misplacements of the trajectory and increases the system’s complexity. In this work, we introduce ISM-FLUX, a novel implementation of MINFLUX using image-scanning microscopy (ISM) with a single-photon avalanche diode (SPAD) array detector. ISM-FLUX provides precise MINFLUX localization within the trajectory while maintaining conventional photon-limited uncertainty outside it. The robustness of ISM-FLUX localization results in a larger localization range and greatly simplifies the architecture, which may facilitate broader adoption of MIN-FLUX.

Breaking Abbe's diffraction limit with harmonic deactivation microscopy
Kevin Murzyn, Maarten L. S. van der Geest, Leo Guery, Zhonghui Nie, Pieter van Essen, Stefan Witte, Peter M. Kraus
arXiv:2403.06617 Preprint (2024)

View Abstract
Nonlinear optical microscopy provides elegant means for label-free imaging of biological samples and condensed matter systems. The widespread areas of application could even be increased if resolution was improved, which is currently limited by the famous Abbe diffraction limit. Super-resolution techniques can break the diffraction limit but rely on fluorescent labeling. This makes them incompatible with (sub-)femtosecond temporal resolution and applications that demand the absence of labeling. Here, we introduce harmonic deactivation microscopy (HADES) for breaking the diffraction limit in non-fluorescent samples. By controlling the harmonic generation process on the quantum level with a second donut-shaped pulse, we confine the third harmonic generation to three times below the original focus size and use this pulse for scanning microscopy. We demonstrate that resolution improvement by deactivation is more efficient for higher harmonic orders, and only limited by the maximum applicable deactivation-pulse fluence. This provides a route towards sub-100~nm resolution in a regular nonlinear microscope. The new capability of label-free super-resolution can find immediate applications in condensed matter physics, semiconductor metrology, and biomedical imaging.

Spatial Confinement of Atomic Excitation in a Doped Solid
Markus Stabel
Dissertation, Technische Universität Darmstadt, Germany

View Abstract
This dissertation explores the spatial control of light-matter interactions in rare-earth-doped solids. A key component of the research involves the use of spiral phase plates to create optical vortices for spatially selective excitation. The work demonstrates that by tailoring the phase and intensity profiles of the driving fields, it is possible to confine atomic populations to volumes far below the diffraction limit, with applications in quantum information storage and high-resolution spectroscopy.

Molecule Localization with STED
Henrik von der Emde
Dissertation, Heidelberg University, Germany

View Abstract
I present a re-implementation of the super-resolution method MINSTED, which enhances the stimulated emission interaction probability of the STED (stimulated emission depletion) process and therefore reduces the optical power required by approximately one order of magnitude. This results in an enhanced localization performance, achieving uncertainties in single-molecule localization below 1nm. This molecular-scale localization precision is applied to biological specimens upon the use of the DNA-PAINT labelling scheme. The imaging of the nuclear pore complex in fixed HeLa cells is demonstrated and the colocalization of synaptic vesicle proteins in a multi-colour experiment in fixed rat hippocampal neurons was investigated. The MINSTED localization approach is additionally shown to be used for single molecule tracking at nanometre-millisecond spatio-temporal precision. The biological relevance is highlighted by tracking of the motor protein kinesin-1, clearly resolving its 16nm steps with a temporal precision of <2ms.

Vortex-comb spectroscopy
Santeri Larnimaa, Markku Vainio
arXiv:2405.09313v1 [physics.optics] 15 May 2024

View Abstract
We propose a new Fourier-transform spectroscopy technique based on the rotational Doppler effect. The technique offers an application for optical vortex frequency combs, where each frequency component carries a unique amount of orbital angular momentum (OAM). Here, we emulate a vortex comb using a tunable single frequency laser and a collection of spiral phase plates, generating up to eleven distinct OAM modes. Unlike in traditional Fourier-transform spectroscopy based on the Michelson interferometer (linear Doppler effect), the spectral resolution of vortex-comb spectroscopy is not limited by the mechanical scan distance of the instrument but only by the measurement time. Although the spectrometer requires just one free-running frequency comb, the down-conversion scheme resembles dual-comb spectroscopy, leading to fast mode-resolved measurements.

2023

MINSTED nanoscopy enters the Ångström localization range
Michael Weber, Henrik von der Emde, Marcel Leutenegger, Philip Gunkel, Sivakumar Sambandan, Taukeer A. Khan, Jan Keller-Findeisen, Volker C. Cordes & Stefan W. Hell
Nature Biotechnology volume 41, pages 569–576 (2023)

View Abstract
Super-resolution techniques have achieved localization precisions in the nanometer regime. Here we report all-optical, room temperature localization of fluorophores with precision in the Ångström range. We built on the concept of MINSTED nanoscopy where precision is increased by encircling the fluorophore with the low-intensity central region of a stimulated emission depletion (STED) donut beam while constantly increasing the absolute donut power. By blue-shifting the STED beam and separating fluorophores by on/off switching, individual fluorophores bound to a DNA strand are localized with σ = 4.7 Å, corresponding to a fraction of the fluorophore size, with only 2,000 detected photons. MINSTED fluorescence nanoscopy with single-digit nanometer resolution is exemplified by imaging nuclear pore complexes and the distribution of nuclear lamin in mammalian cells labeled by transient DNA hybridization. Because our experiments yield a localization precision σ = 2.3 Å, estimated for 10,000 detected photons, we anticipate that MINSTED will open up new areas of application in the study of macromolecular complexes in cells.

Combining pMINFLUX, graphene energy transfer and DNA-PAINT for nanometer precise 3D super-resolution microscopy
Jonas Zähringer, Fiona Cole, Johann Bohlen, Florian Steiner, Izabela Kamińska and Philip Tinnefeld
Light: Science & Applications volume 12, Article number: 70 (2023)

View Abstract
3D super-resolution microscopy with nanometric resolution is a key to fully complement ultrastructural techniques with fluorescence imaging. Here, we achieve 3D super-resolution by combining the 2D localization of pMINFLUX with the axial information of graphene energy transfer (GET) and the single-molecule switching by DNA-PAINT. We demonstrate <2 nm localization precision in all 3 dimension with axial precision reaching below 0.3 nm. In 3D DNA-PAINT measurements, structural features, i.e., individual docking strands at distances of 3 nm, are directly resolved on DNA origami structures. pMINFLUX and GET represent a particular synergetic combination for super-resolution imaging near the surface such as for cell adhesion and membrane complexes as the information of each photon is used for both 2D and axial localization information. Furthermore, we introduce local PAINT (L-PAINT), in which DNA-PAINT imager strands are equipped with an additional binding sequence for local upconcentration improving signal-to-background ratio and imaging speed of local clusters. L-PAINT is demonstrated by imaging a triangular structure with 6 nm side lengths within seconds.

Single-spot spiral phase plate for tracking 3D particle motion
Keith Bonin, Sudhakar Prasad, Will Caulkins, George Holzwarth, Stephen R. Baker, Pierre-Alexandre Vidi
Biophysical Journal, Volume 122, ISSUE 3, SUPPLEMENT 1, 130a-131a (2023)

View Abstract
We have imaged and tracked submicron fluorescent particles in three dimensions by inserting a spiral phase plate (SPP) of our design into a conventional wide-field optical microscope. Our novel SPP consists of concentric annular zones that each impose a unique quantized orbital angular momentum (OAM) on the ring of fluorescent light it intercepts. Each ring of the SPP consists of a vortex surface that produces one additional unit of OAM than the smaller ring just inside it, with the seven successive rings each contributing n = 1 to 7 quantum units of OAM respectively. The light rings interfere to produce a single-spot rotating point spread function (SS-RPSF). This image ‘spot’ rotates with the axial depth of a particle, permitting 3D mapping of the particle position. The SPP is easily incorporated into existing microscopes. We used the DIC slider here for the SPP. 3D positions of fluorescent beads were retrieved using template matching. Bead positions could be inferred over a 6 µm depth range. Best results were obtained over a depth range of 2.3 μm, with a mean absolute error of 20 nm in this range. As proof-of-concept for live-cell imaging we tracked DNA loci and determined their diffusion coefficients in the 3D environment of the nucleus of U2OS cells. We are pursuing chromatin tracking experiments to better understand how DNA damage affects chromatin motions and, reciprocally, how chromatin dynamics impacts the DNA damage response. Beyond this specific application, our SPP-based imaging approach should enable researchers to track dynamic fluorescent objects in samples with high temporal resolution because x, y, and z are determined at exactly the same time.

Optimization and characterization of toroidal foci for super-resolution fluorescence microscopy: tutorial
Lucía F. Lopez, Luciano A. Masullo, Alan M. Szalai, Florencia Edorna, Florencia D. Choque, Fernando Caprile, and Fernando D. Stefani
Journal of the Optical Society of America B Vol. 40, Issue 4, pp. C103-C110 (2023)

View Abstract
Single-molecule localization microscopy (SMLM) has become an essential tool to investigate phenomena at the nanoscale. Among the different SMLM approaches, methods that interrogate the molecular position with an intensity minimum, such as minimal emission fluxes (MINFLUX) or the more recent raster scanning a minimum of light (RASTMIN), stand out for reaching true molecular resolution. To implement these methods, the phase of the excitation beam needs to be modulated to obtain a focus with a central minimum, i.e., a so-called toroidal or doughnut-shaped focus. In this tutorial, we explain the basis and experimental tricks to generate and optimize such beams, particularly in raster-scanning microscopes.

The role of the brain extracellular space in diffusion and cell signalling
Paula Giménez Mínguez
Dissertation, Achucarro Basque Center for Neuroscience

View Abstract
This doctoral thesis investigates the structural properties of the brain's extracellular space (ECS) and its impact on molecular diffusion. By utilizing super-resolution STED microscopy with vortex phase-shaping technology, the research captures the convoluted nanoscale geometry of the ECS in live brain tissue. The work demonstrates how local ECS morphology acts as a direct modulator of extrasynaptic signaling, influencing how neurotransmitters move between neurons and glial cells.

Pulsed-interleaved MINFLUX super-resolution microscopy
Jonas Zähringer
Dissertation, LMU München: Faculty of Chemistry and Pharmacy

View Abstract
Light microscopy has become a powerful tool to investigate structures, dynamics, and interactions in natural science such as cell biology. Especially fluorescence microscopy has seen a rapid development during the last decades. The emergence of far-field fluorescence super-resolution microscopy even overcame the fundamental diffraction limit, enabling imaging with high contrast and specificity of structures below 200 nm. With less than a tenth of the photons needed compared to previous super-resolution methods, MINFLUX is the most recent development to push the resolution limit to truly molecular dimensions. This is achieved by combining the excitation information of a structured illumination featuring a minimum with the respective emission information. While MINFLUX enables the visualization of structures and dynamics with 1 nm precision, the size of a fluorophore, only individual fluorophores are localized, thus information about their environment is missing. The method of choice to report about the environment of a fluorophore is the fluorescence lifetime. To this end, a combination of MINFLUX coupled with the fluorescence lifetime would vastly increase the information wealth of MINFLUX localizations. In this thesis, I built a pulsed-interleaved MINFLUX (pMINFLUX) that extends the nanometer precise localizations of MINFLUX with the fluorescence lifetime domain while additionally simplifying the technological complexity of pMINFLUX. I demonstrated the performance of this setup using DNA origami structures which act as nanoruler. The unprecedented combination of fluorescence lifetime and nanometer precise localizations was employed in four novel methodologies to make the investigation of structures, interactions, dynamics, and their interplay on the nanometer length scale more accessible. In combination with graphene energy transfer (GET), I extended the nanometer precise lateral localizations of MINFLUX to the third dimension, by using the fluorescence lifetime encoded axial distance information for nanometer precise 3D super-resolution microscopy. I demonstrated the resolution of GET-pMINFLUX on DNA origami structures using DNA-PAINT with axial precisions below 0.4 nm. DNA-PAINT was used to generate stochastic blinking, which is necessary for the localization method MINFLUX to resolve distances smaller than the diffraction limit. To increase the imaging speed and overcome issues with high fluorescent background of DNA-PAINT, I established local-PAINT (L-PAINT). In contrast to DNA-PAINT, L-PAINT imager strands have two binding sequences with a designed binding hierarchy such that the L-PAINT DNA-strand binds longer on one side. This allows the fluorescent dye-modified second end of the strand to locally scan for binding sites at a rapid rate. While MINFLUX is able to give insight into structural information, the interplay with the environment remains unknown as only individual fluorophores are localized. I addressed this problem by first combining Förster resonance energy transfer (FRET) with MINFLUX to simultaneously localize the donor dye and map the distance to an acceptor dye. With the multilateration of several donor dye positions I localized the acceptor dye with a full width half maximum of 0.17 nm. To overcome the limited working range of FRET of 2-10 nm, I developed a pMINFLUX lifetime multiplexing approach. pMINFLUX lifetime multiplexing uses the fluorescence lifetime to colocalize two spectrally similar dyes without photo-switching over a large field-of-view. Beyond the FRET range, pMINFLUX lifetime multiplexing enabled the co-localization of two dyes by separating their fluorescence intensities according to their fluorescence lifetimes. I demonstrated this in simulation and experiment using two independent L-PAINT pointer systems, whose dynamics were imaged with nanometer precision. Inside the FRET range, two dyes were co-localized using a newly developed combined phasor-microtime gating approach. As a result, the combination of both multiplexing approaches closed the resolution gap between single-molecule FRET and co-tracking.

Dual spatio-temporal regulation of axon growth and microtubule dynamics by RhoA signaling pathways
José Wojnacki, Gonzalo Quassollo, Martín D. Bordenave, Nicolás Unsain, Gaby F. Martínez, Alan M. Szalai, Olivier Pertz, Gregg G. Gundersen, Francesca Bartolini, Fernando D. Stefani, Alfredo Cáceres, Mariano Bisbal
bioRxiv, preprint (2023)

View Abstract
RhoA plays a crucial role in neuronal polarization, where its action restraining axon outgrowth has been thoroughly studied. We now report that RhoA has not only inhibitory but also a stimulatory effect on axon development depending on when and where exerts its action and the downstream effectors involved. In cultured hippocampal neurons, FRET imaging revealed that RhoA activity selectively localizes in growth cones of undifferentiated neurites, while in developing axons it displays a biphasic pattern, being low in nascent axons and high in elongating ones. RhoA-Rho kinase (ROCK) signaling prevents axon initiation but has no effect on elongation, while formin inhibition reduces axon extension without significantly altering initial outgrowth. Besides, RhoA-mDia promotes axon elongation by stimulating growth cone microtubule stability and assembly, as opposed to RhoA-ROCK that restrains growth cone microtubule assembly and protrusion. Finally, we show that similar mechanisms might operate during axonal regeneration, with RhoA-ROCK slowing axon regrowth after axotomy and RhoA-mDia favoring extension of regenerated axons.

2022

Colocalization of different neurotransmitter transporters on synaptic vesicles is sparse except for VGLUT1 and ZnT3
Neha Upmanyu, Jialin Jin, Henrik von der Emde, et al.
Neuron 110, 1483–1497

View Abstract
Vesicular transporters (VTs) define the type of neurotransmitter that synaptic vesicles (SVs) store and release. While certain mammalian neurons release multiple transmitters, it is not clear whether the release occurs from the same or distinct vesicle pools at the synapse. Using quantitative single-vesicle imaging, we show that a vast majority of SVs in the rodent brain contain only one type of VT, indicating specificity for a single neurotransmitter. Interestingly, SVs containing dual transporters are highly diverse (27 types) but small in proportion (2% of all SVs), excluding the largest pool that carries VGLUT1 and ZnT3 (34%). Using VGLUT1-ZnT3 SVs, we demonstrate that the transporter colocalization influences the SV content and synaptic quantal size. Thus, the presence of diverse transporters on the same vesicle is bona fide, and depending on the VT types, this may act to regulate neurotransmitter type, content, and release in space and time.

Conservation of orbital angular momentum and polarization through biological waveguides
Nicolas Perez, Daryl Preece, Robert Wilson & Anna Bezryadina
Sci Rep 12, 14144

View Abstract
A major roadblock to the development of photonic sensors is the scattering associated with many biological systems. We show the conservation of photonic states through optically self-arranged biological waveguides, for the first time, which can be implemented to transmit light through scattering media. The conservation of optical properties of light through biological waveguides allows for the transmission of high bandwidth information with low loss through scattering media. Here, we experimentally demonstrate the conservation of polarization state and orbital angular momentum of light through a self-arranged biological waveguide, several centimeters long, in a sheep red blood cell suspension. We utilize nonlinear optical effects to self-trap cells, which form waveguides at 532 nm and 780 nm wavelengths. Moreover, we use the formed waveguide channels to couple and guide probe beams without altering the information. The formed biological waveguides are in a sub-diffusive scattering regime, so the photons’ information degrades insignificantly over several centimeters of propagation through the scattering media. Our results show the potential of biological waveguides as a methodology for the development of novel photonic biosensors, biomedical devices that require optical wireless communication, and the development of new approaches to noninvasive biomedical imaging.

Excitation of an Electric Octupole Transition by Twisted Light
R. Lange, N. Huntemann, A. A. Peshkov, A. Surzhykov, and E. Peik
Phys. Rev. Lett. 129, 253901

View Abstract
We study the coherent excitation of the S1/22→F7/22 electric octupole (E3) transition by twisted light modes with a single Yb+171 ion in the dark center of a vortex beam. The intensity distribution of the beam is mapped as a function of the ion’s position by measuring the light shift on an auxiliary electric quadrupole transition. In the center of the vortex beam, we observe excitation of the E3 transition with a fivefold reduced light shift in comparison to excitation by plane wave radiation for the same Rabi frequency. We measure the excitation probabilities for Laguerre-Gaussian twisted light modes of first and second order for different polarization patterns at various orientations of the ion quantization axis with respect to the beam propagation vector. We compare the experimental results with theoretical predictions and find good qualitative agreement.

An alternative to MINFLUX that enables nanometer resolution in a confocal microscope
Luciano A. Masullo, Alan M. Szalai, Lucía F. Lopez, Mauricio Pilo-Pais, Guillermo P. Acuna and Fernando D. Stefani
Light: Science & Applications volume 11, Article number: 199

View Abstract
Localization of single fluorescent emitters is key for physicochemical and biophysical measurements at the nanoscale and beyond ensemble averaging. Examples include single-molecule tracking and super-resolution imaging by single-molecule localization microscopy. Among the numerous localization methods available, MINFLUX outstands for achieving a ~10-fold improvement in resolution over wide-field camera-based approaches, reaching the molecular scale at moderate photon counts. Widespread application of MINFLUX and related methods has been hindered by the technical complexity of the setups. Here, we present RASTMIN, a single-molecule localization method based on raster scanning a light pattern comprising a minimum of intensity. RASTMIN delivers ~1–2 nm localization precision with usual fluorophores and is easily implementable on a standard confocal microscope with few modifications. We demonstrate the performance of RASTMIN in localization of single molecules and super-resolution imaging of DNA origami structures.

Twisted light Michelson interferometer for high precision refractive index measurements
Nicola M. Kerschbaumer, et al.
Optics Express Vol. 30, Issue 16, pp. 29722-29734

View Abstract
Using orbital angular momentum beams in a Michelson interferometer opens the possibility for non-invasive measurements of refractive index changes down to 10−6 refractive index units. We demonstrate the application of a twisted light interferometer to directly measure the concentration of NaCl and glucose solutions label-free and in situ and to monitor temperature differences in the mK-µK range. From these measurements we can extract a correlation of the refractive index to concentration and to temperature from a liquid sample which is in good agreement with literature. Applying this type of twisted light interferometry yields a novel, robust, and easily implementable method for in situ monitoring of concentration and temperature changes in microfluidic samples.

Three-dimensional tracking using a single-spot rotating point spread function created by a multiring spiral phase plate
Keith Bonin, et al.
Journal of Biomedical Optics, Vol. 27, Issue 12, 126501

View Abstract
We describe a single-spot 3D tracking method using a rotating point spread function (PSF) created by a multiring spiral phase plate (MSPP). The MSPP is designed to produce a PSF with a single high-intensity spot that rotates as a function of the emitter's axial (z) position. This allows for high-speed tracking of particles in 3D with a standard camera. We demonstrate the precision of the method by tracking fluorescent beads in glycerol and genomic loci in live cells, achieving nanometer-scale localization in all three dimensions.

Confining atomic populations in space via stimulated Raman adiabatic passage in a doped solid
Markus Stabel, Leo Daniel Feldmann and Thomas Halfmann
J. Phys. B: At. Mol. Opt. Phys. 55 154003

View Abstract
We experimentally demonstrate spatial confinement of atomic excitation by adiabatic passage processes in a rare-earth ion-doped Pr3+:Y2SiO5 crystal. In particular, we apply stimulated Raman adiabatic passage (STIRAP) and compare its performance with electromagnetically induced transparency (EIT). Using a Stokes beam with Gaussian and a pump beam with donut shape we localize the atomic population in the zero-intensity center of the latter. Our data confirm that adiabatic passage confines excitation far below the diameter of the driving laser beams, and that this localization rapidly increases with laser intensity. We find, that STIRAP significantly outperforms EIT, as it was predicted by previous theory proposals, i.e., STIRAP reaches small excitation volumes with much lower laser intensity. The experimental data agree very well with numerical simulations. The findings serve as a step towards new applications for STIRAP, to prepare excitation regions or population patterns in space with large resolution.

Wavelength-tunable spiral-phase-contrast imaging
Dong-Ho Lee, et al.
Optics Express Vol. 30, Issue 15, pp. 27273-27284

View Abstract
Wavelength-tunable spiral-phase-contrast (SPC) imaging was experimentally accomplished in the visible wavelengths spanning a broad bandwidth of ∼200 nm based on a single off-axis spiral phase mirror (OSPM). By the rotation of an OSPM, which was designed with an integer orbital angular momentum (OAM) of l = 1 at a wavelength of 561 nm and incidence angle of 45°, high-quality SPC imaging was obtained at different wavelengths. For the comparison with wavelength-tunable SPC imaging using an OSPM, SPC imaging using a spiral phase plate (manufactured to generate an OAM of l = 1 at 561 nm) was performed at three wavelengths (473, 561, and 660 nm), resulting in clear differences. Theoretically, based on field tracing simulations, high-quality wavelength-tunable SPC imaging could be demonstrated in a very broad bandwidth of ∼400 nm, which is beyond the bandwidth of ∼200 nm obtained experimentally. This technique contribute to developing high-performance wavelength-tunable SPC imaging by simply integrating an OSPM into the current optical imaging technologies.

Spatiotemporal sampling of near-petahertz vortex fields
Johannes Blöchl, et al.
Optica Vol. 9, Issue 7, pp. 755-761

View Abstract
Measuring the field of visible light with high spatial resolution has been challenging, as many established methods only detect a focus-averaged signal. Here, we introduce a near-field method for optical field sampling that overcomes that limitation by employing the localization of the enhanced near-field of a nanometric needle tip. A probe field perturbs the photoemission from the tip, which is induced by a pump pulse, generating a field-dependent current modulation that can easily be captured with our electronic detection scheme. The approach provides reliable characterization of near-petahertz fields. We show that not only the spiral wavefront of visible femtosecond light pulses carrying orbital angular momentum (OAM) can be resolved but also the field evolution with time in the focal plane. Additionally, our method is polarization sensitive, which makes it applicable to vectorial field reconstruction.

Ptychographic characterization of extreme ultraviolet vortex beams
Antonios Pelekanidis, et al.
Optica Publishing Group, paper CF1D.7

View Abstract
We generate multi-wavelength extreme-ultraviolet vortex beams via high-harmonic generation. We characterize the wavefronts of these high orbital angular mo-mentum beams using ptychography.

Radiative Cooling and Optical Temperature Sensing
Nicola Mara Kerschbaumer
Dissertation, LMU Muenchen

View Abstract
Temperature and light are intrinsically related to each other. Thermal radiation impacts temperature and temperature impacts optical properties of materials. The aim of this work is to use this relationship to radiatively cool down bodies on the one hand and to employ light for a novel temperature sensing method on the other hand. Over the course of the last years, the concept of passive radiative cooling has become a topic of considerable interest for applications in the context of thermal building management and energy saving. In this field, nanophotonic surfaces are engineered to emit thermal radiation in the atmospheric window, while simultaneously reflecting sunlight. The result is a net cooling effect that does not require energy input. This cooling can be further enhanced when considering the possibility to systematically direct thermal radiation, i.e., electromagnetic waves with the aid of optical elements. Prior to this work, the idea to focus thermal radiation for contactless cooling was only scarcely explored. In the first half of this work an elliptical mirror is applied to increase the view factor of radiative heat transfer by a factor of 92. With this approach various samples are cooled down radiatively and spatially structured cooling patterns are generated on their surfaces. First applications exploiting this cooling pathway even include the supercooling of liquids. In the second half of this thesis a novel method for ultra-precise temperature measurements is introduced. In this case temperature is used to manipulate radiation. This concept relies on the temperature-dependence of the refractive index, which in turn influences radiation passing through a medium. To utilize this dependence, an interferometer in a Michelson configuration is built and transparent liquid samples are placed in one of the arms. Twisted light modes containing orbital angular momentum are used, since interfering such beams with opposing helicity yields an interference pattern, which is sensitive to any phase change, i.e., any refractive index change of the observed sample. With this setup refractive index changes on the order of 10-7 can be resolved. Besides the already mentioned temperaturedependence, the refractive index also relies on the concentration of the liquid samples. Both of these parameters are studied independently and the interferometer achieves resolutions in the µK and µM range for temperature and concentration measurements, respectively. Applying this type of twisted light interferometry yields a novel, robust and easily implemented method for in situ temperature and concentration monitoring in liquid samples.

2021

Simultaneous orientation and 3D localization microscopy with a Vortex point spread function
Christiaan N. Hulleman, Rasmus Ø. Thorsen, Eugene Kim, Cees Dekker, Sjoerd Stallinga & Bernd Rieger
Nature Communications volume 12, Article number: 5934

Pulsed Interleaved MINFLUX
Luciano A. Masullo, Florian Steiner, Jonas Zähringer, Lucía F. Lopez, Johann Bohlen, Lars Richter, Fiona Cole, Philip Tinnefeld, and Fernando D. Stefani
Nano Lett. 2021, 21, 1, 840–846

Super-resolution Imaging of Energy Transfer by Intensity-Based STED-FRET
Alan M. Szalai, Bruno Siarry, Jerónimo Lukin, Sebastián Giusti, Nicolás Unsain, Alfredo Cáceres, Florian Steiner, Philip Tinnefeld, Damián Refojo, Thomas M. Jovin, and Fernando D. Stefani
Nano Lett. 2021, 21, 5, 2296–2303

Background suppression with dual modulation by saturated absorption competition microscopy
Chuankang Li, Renjie Zhou, Wensheng Wang,Zhengyi Zhan, Zhimin Zhang, Yuhang Li, Yuzhu Li ,Xiang Hao Cuifang,Kuang, Xu Liu
Optics and Lasers in Engineering Volume 147, December 2021, 106750

Ptychographic characterization of extreme ultraviolet vortex beams
Antonios Pelekanidis, Lars Loetgering, and Stefan Witte
OSA Technical Digest (Optica Publishing Group, 2021), paper CTu6A.1

Photon-efficient fluorescence nanoscopy by scanning light intensity minima
Luciano Masullo
Dissertation, University of Buenos Aires

Field-resolved studies of ultrafast light-matter interaction
Johannes Schoetz
Dissertation, LMU Muenchen, Fakultaet für Physik

Localization microscopy of constrained fluorescent molecules Pushing towards Ångström-scale resolution through cryogenics
Christiaan Hulleman
Dissertation, Delft University of Technology

Parameter estimation in single molecule microscopy
Rasmus Thorsen
Dissertation, Delft University of Technology

2020

Pulsed Interleaved MINFLUX
Luciano A. Masullo, Florian Steiner, Jonas Zähringer, Lucía F. Lopez, Johann Bohlen, Lars Richter,Fiona Cole, Philip Tinnefeld and Fernando D. Stefani
Nano Lett. 2021, 21, 1, 840–846

Widefield quantitative phase imaging by second-harmonic dispersion interferometry
Fernando Brandi and Frank Wessel
Optics Letters Vol. 45, Issue 15, pp. 4304-4307

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