arXiv subjects

Marcus Ossiander

Publications and source records attributed to Marcus Ossiander.

17 recordsLinked to original sources

arXiv2026

A swept-source dual-comb spectrometer on a chip

Dual-comb spectroscopy (DCS) enables high-speed, high-resolution spectroscopy by down-converting optical spectra to the radio-frequency (RF) domain through the interference of two mutually detuned frequency combs. Accurately resolving narrow molecular absorption features requires closely spaced comb lines generated by large laser cavities with long round-trip times, thereby hindering the miniaturization of high-resolution spectrometers. Here, we circumvent this limitation by demonstrating a swept-source dual-comb spectrometer using two unidirectional racetrack semiconductor lasers integrated on the same chip. The traveling-wave frequency combs are generated by strong RF injection at the laser cavity round-trip frequency of 14.3~GHz and are continuously tuned in frequency by varying the laser drive currents. This enables continuous spectral sampling over a 32~cm$^{-1}$ range centered near 8~\textmu m, with an effective sampling interval of approximately 80~MHz. The outputs of both combs are coupled into the same monolithically integrated light coupler, providing automatic collinear alignment before the combined beam interrogates the sample. We benchmark the spectrometer against an external-cavity tunable laser and validate its performance using HITRAN simulations for 1.25\% nitrous oxide. Finally, the unidirectional comb architecture suppresses the detrimental effects of optical feedback, yielding comparable residuals even under deliberately introduced strong feedback. More broadly, the benefits of miniaturization extend beyond reduced footprint: chip-scale integration enables new forms of electrical and optical control that can fundamentally change how dual-comb spectrometers are operated.

physics.optics↗

arXiv2026

Hybrid BaTiO3/TiO2 Metasurface for Efficient Gigahertz-Speed Free-Space Electro-Optic Modulation

Free-space electro-optic modulators are key to emerging photonic systems, yet their performance remains limited by trade-offs between modulation efficiency, bandwidth, and device aperture. Here we report a hybrid BaTiO3 (BTO)/TiO2 metasurface for large-aperture, efficient, gigahertz-speed free-space electro-optic modulation. Combining scalable BTO film growth by radio-frequency magnetron sputtering with mature TiO2 nanofabrication, we pattern the metasurface in TiO2 on an unetched BTO layer. The resulting devices support guided-mode resonances with quality factors exceeding 1300 and an optical confinement factor of ~0.8, while the continuous BTO layer makes efficient use of the applied voltage, together maximizing the overlap between the optical and driving fields within the BTO. A device with a 0.3 mm x 0.3 mm metasurface achieves a transmittance modulation efficiency of ~0.020 per volt and a -3 dB electro-optic bandwidth of ~0.8 GHz, with an effective Pockels coefficient of ~151 pm/V for the BTO. This establishes a scalable route to high-performance free-space electro-optic modulators for LiDAR, free-space optical communication, and reconfigurable optical computing.

physics.optics↗

arXiv2026

Transmissive extreme ultraviolet metagrating

Extreme ultraviolet (EUV) radiation is a key tool for attosecond physics and lithography. However, strong material absorption limits the availability of transmissive optical elements at these wavelengths. Metaoptics exploit geometry to control the wavefront of transmitted light on the nanoscale and, due to their minimal thickness, promise to fill this gap. Here, we demonstrate the first EUV metaoptics for broadband applications: we design, fabricate, and experimentally investigate a blazed transmissive EUV metagrating and compare it with a focused-ion-beam-milled sawtooth-blazed grating serving as an in-situ reference. The metagrating achieves an angular dispersion of 0.04{\deg}/nm with a directionality (the ratio of the +1st and -1st diffraction order efficiency) of up to 5.8. The device shows phase-based operation up to 50 eV photon energy (down to 25 nm vacuum wavelength) and an octave-spanning bandwidth of 25 eV, doubling the previous spectral window addressable by metasurfaces. Comparing both gratings' performance reveals that, when accounting for fabrication constraints, EUV metasurfaces are competitive with free-form optics while offering scalability to large apertures and arbitrary phase profiles. Broadband transmissive operation removes the need for grazing incidence optics, defeating a major source of aberrations, and allows polarization-insensitive spectral analysis, enabling energy-resolved ultrafast spectroscopy in compact experimental configurations.

physics.optics↗

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2026

Quantum-Well-Metasurface to Maximize Nonlinear Polarization

Nonlinear frequency conversion unlocks technologies ranging from telecommunications to quantum computation; however, weak nonlinearities and architectures that resist miniaturization currently limit devices. Here, we combine a bandstructure-engineered GaAs/AlGaAs heterostructure with a high quality factor dielectric metasurface to simultaneously tailor the intrinsic nonlinear susceptibility and optimize the electromagnetic field within the heterostructure. By engineering a resonant interband transition, we realize a large second-order nonlinear tensor element, 1.6 nm/V at 1.57 um wavelength. We then make it free-space-accessible and boost the effective nonlinearity to ~ 14 nm/V using a metasurface patterned on the material. Our proof-of-concept experiment establishes that interband transition engineering and metasurfaces accessing otherwise unusable nonlinear tensor elements enable giant effective nonlinearities in the near-infrared to visible spectrum. This addresses material and device-level constraints in nonlinear photonics, providing a scalable route to compact, efficient devices.

physics.optics↗

arXiv2026

Multimode Single-Ring Photonic Molecule

Photonic molecules can mimic interactions of atomic energy levels, offering new ways to manipulate cavity eigenstates. Current methods using evanescent coupling of multiple cavities face challenges in scalability, flexibility, and coupling control, especially for complex systems. Here we introduce a new method that uses a single multimode optical ring resonator to create photonic molecules. Our design uses multiple waveguide transverse modes in one resonator, providing flexibility to engineer complex interactions without typical coupling constraints. We demonstrate arbitrary inter-mode coupling through transmissive mode converters, allowing precise tuning of resonance splitting and intrinsic losses. This approach enables selective bright-dark mode pair generation and the exploration of novel photonic phenomena such as exceptional points. This multimode photonic molecule overcomes traditional limitations and offers new possibilities for integrated photonic circuits, optical processing, and studies in non-Hermitian and nonlinear photonics.

physics.optics↗

arXiv2025

NIR/VIS dual-comb spectroscopy comparing high and low repetition rate regimes

Dual-comb spectroscopy enables broadband analysis of key molecules with unparalleled frequency resolution and exceptional signal-to-noise ratios across various spectral regions. However, fully harnessing its potential for broadband spectroscopy with high sensitivity and spectral resolution depends critically on selecting the appropriate frequency combs with optimized (comb) parameters tailored to specific applications. This study compares dual-comb spectroscopy systems operating at 80 MHz and 1 GHz repetition rates, in the near infrared and visible spectral regions. The 80 MHz system provides high spectral resolution, ideal for resolving complex spectra, showcased with measurements of NH$_3$ vibrational bands and I$_2$ hyperfine transitions. Utilizing phase-locked feed-forward stabilization, the system delivers excellent signal-to-noise ratios but faces limitations in temporal resolution. The free-running 1 GHz system offers superior temporal resolution and compactness, making it suitable for real-time environmental monitoring in laboratory and field settings. A self-correction algorithm advances the high mutual coherence, enabling high-signal-to-noise measurements without additional electronics. With its 1 GHz resolution, it excels in monitoring NH$_3$ transitions or NO$_2$ lines at high speeds. This work highlights the complementary strengths of these systems for high-resolution spectroscopy and real time trace gas sensing.

physics.optics↗

arXiv2025

Streaming Self-Corrected Dual-Comb Spectrometer

We radically simplify coherently averaged dual-comb spectroscopy by introducing a real-time self-correction system: a radio frequency system-on-chip computes each incoming dual-comb interferogram's phase, frequency, and arrival time; calculates changes in the combs' carrier-envelope offset frequency and repetition rate difference; and immediately phase-corrects the incoming interferogram data stream. The algorithm supports up to 0.3 GHz interferogram frequency bandwidth and thus combines fast measurement times (corresponding to high detunings) with broadband optical detection. Using this system, we achieve comb-resolved spectroscopy with Fourier-limited linewidth, coherent averaging over arbitrarily long durations, and high signal-to-noise ratios (e.g., up to 2900 for 150 s averaging time). Iodine and acetylene spectroscopy yield excellent agreement with literature over an optical bandwidth of 10 THz in the visible and near-infrared. Common dual-comb spectroscopy self-correction requires a bright and continuous interferogram train. We lift this requirement by introducing cross-channel correction: the algorithm measures phase fluctuations from a reference channel and predicts and corrects their influence on a signal channel. This enables correcting unstable or intermittent signals (typical, e.g., in field measurements), or low-amplitude signals with amplified phase fluctuations (relevant for nonlinearly upconverted combs). The approach makes instantaneous dual-comb spectroscopy available to everyday applications.

physics.optics↗

arXiv2024

Photoacoustic microscopy with meta-optics

Recent advances in the miniaturization of optical elements have led to the emergence of novel imaging systems, used for industrial and consumer-based applications. The underlying methods are particularly prevalent in the realms of medical imaging and optical microscopy. Avoiding bulky optical elements can be extremely beneficial to many microscopy modalities, one of which is photoacoustic microscopy. Relying on short, highly focused light pulses that need to be precisely controlled, large and heavy optical elements can often hinder the overall performance of such systems. We propose the utilization of increasingly popular optical elements, so-called meta-optics, in the excitation path of a photoacoustic microscope. The metalenses, which were designed and used for this work, consist of sub-wavelength elements that enable elaborate phase control of incident light and multifunctionality within a single optical element. This allowed us to not only replace common optical elements in the excitation path of the photoacoustic microscope, completely omitting any conventional glass elements, but also to design an adapted lens, increasing the depth of field. With our work, we prove the benefit of meta-optics for photoacoustic microscopy by comparing two different metalenses to a conventional glass lens in simulations as well as experiments. We expect this to be a step into the direction of more advanced meta-optics being utilized in photoacoustic imaging setups.

physics.optics↗

arXiv2024

Phase-locked feed forward stabilization for dual comb spectroscopy

Sustained mutual coherence between two combs over extended periods is a prerequisite for dual-comb spectroscopy (DCS), particularly in achieving high-resolution molecular spectroscopy and precise spectral measurements. However, achieving long coherence times remains a challenge for Yb-doped frequency combs. This work introduces an experimental approach for phase-stable DCS using Yb-doped frequency combs at 1.03 ${\mu}$m with a novel feed-forward method, combatting the limitations of mutual coherence. Without relying on computer-based phase correction, we achieve a coherence time of 1000 seconds - three orders of magnitude longer than the current state of the art for DCS. This extended coherence enables time-domain averaging, resulting in a signal-to-noise ratio (SNR) of 2045. We demonstrate high-resolution monitoring of weak overtone transitions in the P and R branches of C${_2}$H${_2}$, with good agreement with HITRAN. The phase-locked multiheterodyne system also enables phase spectrum measurements with a scatter down to 7 mrad. Furthermore, we successfully extend our technique to the visible wavelength range using second harmonic generation, achieving high-resolution spectra of NO${_2}$ with excellent SNR. The method offers high-frequency accuracy and demonstrates the potential of Yb-doped systems for multiplexed metrology, effectively extending the capabilities of DCS as a powerful tool for multi-disciplinary applications.

physics.optics↗

arXiv2024

Cascaded-mode interferometers: spectral shape and linewidth engineering

Interferometers are essential tools to measure and shape optical fields, and are widely used in optical metrology, sensing, laser physics, and quantum mechanics. They superimpose waves with a mutual phase delay, resulting in a change in light intensity. A frequency-dependent phase delay then allows to shape the spectrum of light, which is essential for filtering, routing, wave shaping, or multiplexing. Simple Mach-Zehnder interferometers superimpose spatial waves and typically generate an output intensity that depends sinusoidally on frequency, limiting the capabilities for spectral engineering. Here, we present a novel framework that uses the interference of multiple transverse modes in a single multimode waveguide to achieve arbitrary spectral shapes in a compact geometry. Through the design of corrugated gratings, these modes couple to each other, allowing the exchange of energy similar to a beam splitter, facilitating easy handling of multiple modes. We theoretically and experimentally demonstrate narrow-linewidth spectra with independently tunable free spectral range and linewidth, as well as independent spectral shapes for various transverse modes. Our methodology can be applied to orthogonal optical modes of different orders, polarization, and angular momentum, and holds promise for sensing, optical metrology, calibration, and computing.

physics.optics↗

arXiv2023

Metasurface-controlled holographic microcavities

Optical microcavities confine light to wavelength-scale volumes and are a key component for manipulating and enhancing the interaction of light, vacuum states, and matter. Current microcavities are constrained to a small number of spatial mode profiles. Imaging cavities can accommodate complicated modes but require an externally pre-shaped input. Here, we experimentally demonstrate a visible-wavelength, metasurface-based, holographic microcavity that overcomes these limitations. The micron-scale metasurface cavity fulfills the round-trip condition for a designed mode with a complex-shaped intensity profile and thus selectively enhances light that couples to this mode, achieving a spectral bandwidth of 0.8 nm. By imaging the intracavity mode, we show that the holographic mode changes quickly with the cavity length, and the cavity displays the desired spatial mode profile only close to the design cavity length. When placing a metasurface on a distributed Bragg reflector and realizing steep phase gradients, the correct choice of the reflector's top layer material can boost metasurface performance considerably. The applied forward-design method is readily transferable to other spectral regimes and mode profiles.

physics.optics↗

arXiv2023

All-glass 100 mm Diameter Visible Metalens for Imaging the Cosmos

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, NA=0.32) using deep-ultraviolet (DUV) projection lithography. Our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. Additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are unique to such large area metasurfaces. We demonstrate direct astronomical imaging of the Sun, the Moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications.

physics.optics↗

arXiv2022

High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale

Achieving high repeatability and efficiency in laser-induced strong shock wave excitation remains a significant technical challenge, as evidenced by the extensive efforts undertaken at large-scale national laboratories to optimize the compression of light element pellets. In this study, we propose and model a novel optical design for generating strong shocks at a tabletop scale. Our approach leverages the spatial and temporal shaping of multiple laser pulses to form concentric laser rings on condensed matter samples. Each laser ring initiates a two-dimensional focusing shock wave that overlaps and converges with preceding shock waves at a central point within the ring. We present preliminary experimental results for a single ring configuration. To enable high-power laser focusing at the micron scale, we demonstrate experimentally the feasibility of employing dielectric metasurfaces with exceptional damage threshold, experimentally determined to be 1.1 J/cm2, as replacements for conventional optics. These metasurfaces enable the creation of pristine, high-fluence laser rings essential for launching stable shock waves in materials. Herein, we showcase results obtained using a water sample, achieving shock pressures in the gigapascal (GPa) range. Our findings provide a promising pathway towards the application of laser-induced strong shock compression in condensed matter at the microscale.

physics.optics↗

arXiv2022

Topologically protected four-dimensional optical singularities

Optical singularities play a major role in modern optics and are frequently deployed in structured light, super-resolution microscopy, and holography. While phase singularities are uniquely defined as locations of undefined phase, polarization singularities studied thus far are either partial, i.e., bright points of well-defined polarization, or unstable for small field perturbations. We demonstrate for the first time a complete, topologically protected polarization singularity; it is located in the 4D space spanned by the three spatial dimensions and the wavelength and is created in the focus of a cascaded metasurface-lens system. The field Jacobian plays a key role in the design of such higher-dimensional singularities, which can be extended to multidimensional wave phenomena, and pave the way to novel applications in topological photonics and precision sensing.

physics.optics↗

arXiv2018

Petahertz Spintronics

The enigmatic coupling between electronic and magnetic phenomena was one of the riddles propelling the development of modern electromagnetism. Today, the fully controlled electric field evolution of ultrashort laser pulses permits the direct and ultrafast control of electronic properties of matter and is the cornerstone of light-wave electronics. In sharp contrast, because there is no first order interaction between light and spins, the magnetic properties of matter can only be affected indirectly on the much slower tens-of-femtosecond timescale in a sequence of optical excitation followed by the rearrangement of the spin structure. Here we record an orders of magnitude faster magnetic switching with sub-femtosecond response time by initiating optical excitations with near-single-cycle laser pulses in a ferromagnetic layer stack. The unfolding dynamics are tracked in real-time by a novel attosecond time-resolved magnetic circular dichroism (atto-MCD) detection scheme revealing optically induced spin and orbital momentum transfer (OISTR) in synchrony with light field driven charge relocation. In tandem with ab-initio quantum dynamical modelling, we show how this mechanism provides simultaneous control over electronic and magnetic properties that are at the heart of spintronic functionality. This first incarnation of attomagnetism observes light field coherent control of spin-dynamics in the initial non-dissipative temporal regime and paves the way towards coherent spintronic applications with Petahertz clock rates.

physics.app-ph↗

arXiv2014

Optical study of lithographically defined, subwavelength plasmonic wires and their coupling to embedded quantum emitters

We present an optical investigation of surface plasmon polaritons propagating along nanoscale Au-wires, lithographically defined on GaAs substrates. A two-axis confocal microscope was used to perform spatially and polarization resolved measurements in order to confirm the guiding of surface plasmon polaritons over lengths ranging from $5-20 μm$ along nanowires with a lateral dimension of only $\approx 100 nm$. Finite difference time domain simulations are used to corroborate our experimental observations and highlight the potential to couple proximal quantum dot emitters to propagating plasmon modes in such extreme sub-wavelength devices. Our findings are of strong relevance for the development of semiconductor based integrated plasmonic and active quantum plasmonic nanosystems that merge quantum emitters with nanoscale plasmonic elements.

cond-mat.mes-hall↗