Publications

DOI:

10.1201/9781003528371-10External link

University Bibliography Jena:

fsu_mods_00036324External link

The application of AI-based methods to the behavioural description of physical systems is often limited by insufficient interpretability and the large amounts of training data required for reliable generalisation. The identification of complexity-moderated model architectures is commonly performed using statistical search techniques, such as genetic algorithms, which are computationally expensive and frequently produce black-box models. This work presents a formal-analogy-based strategy for simplifying the development of machine-learning models for physics-inspired, particularly optics-motivated, problems by exploiting structural properties of corresponding deterministic models. The proposed framework introduces a graph-based intermediate representation between a deterministic model and its machine-learning counterpart. The deterministic model is expressed as a computation graph, from which the relevant functional relations are extracted through a graph-embedding procedure. By assigning trainable parameters to the resulting graph, the representation is transformed into a statistical model. The applicability of the framework is demonstrated through the estimation of optical-fibre eigenmodes from intensity-distribution measurements, the interpretation of white-light interferometric measurements below the Nyquist limit, and the estimation of refractive indices from interferometric data through the analysis of intrinsic model states. The framework is further applied to the formal analysis of model representations, resulting in a conjecture linking descriptive complexity and statistical model capacity. Based on this construction, practical limits of optimally generalising models are analysed and the analogy-based approach is theoretically justified.

DOI:

10.22032/dbt.70654External link

University Bibliography Jena:

fsu_mods_00037775External link

Spectral sensing has been widely employed in applications ranging from satellite-based remote imaging to biomedicine and precision agriculture. However, broader deployment has been constrained by the complexity and cost of traditional hyperspectral instrumentation. In recent years, efforts have shifted toward the development of compact spectrometers targeting specific spectral regions, often at the expense of broadband analytical capability. In this work, we present the proof-of-concept for an integrated multispectral sensor array for broadband spectral applications, combining Silicon- and GaSb-based photodetectors. Spectral selectivity across the VIS/NIR/SWIR spectral domain (400–2300 nm) is enabled with 19 bandpass dielectric filters in a combined active footprint of 2.02 mm². The sensor assessed in this work was specifically designed to evaluate the optimal harvest time based on weekly spectral measurements from multiple apple cultivars, without the need for destructive chemical analysis. Moreover, we demonstrate a deterministic method that employs a high-scattering region in the NIR as an internal normalization reference, enabling the resolution of temporally evolving spectral signatures associated with carotenoids, anthocyanins, chlorophylls, starch, and moisture content. These results demonstrate that broadband spectral sensors can be deployed at scale in agricultural monitoring with multi-crop validation, enhancing field yield potential and reducing post-harvest losses.

DOI:

10.1038/s44310-026-00132-6External link

University Bibliography Jena:

fsu_mods_00036690External link

Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under electric dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high-temperature fabrication processes. In this work, heterostructures made of two distinct amorphous materials, namely SiO ₂ and TiO ₂ , were prepared through plasma-enhanced atomic layer deposition (PEALD) with deposition temperature of 100 °C. By using the uniaxial dispersion model, we characterized the form birefringence of the deposited films, which can play a crucial role for the phase-matching condition in nonlinear waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective bulk second-order susceptibility, (Formula presented.) = 1.30 ± 0.13 pm/V, at a wavelength of 1032 nm. Noteworthy, we observed strong SHG signals from two-component nanolaminates, which are several orders of magnitude larger than those from single layers. The SHG signals from our samples only require the broken inversion symmetry at the interface. Here, optical properties of nanocomposites can be precisely engineered using the promising PEALD technology.

DOI:

10.3390/coatings16040424External link

University Bibliography Jena:

fsu_mods_00035974External link

A systematic exploration of amorphous ABC heterostructures revealed that nanoscale morphological modifications markedly improved their artificial bulk second-order susceptibility. These amorphous birefringent heterostructures were fabricated using plasma-enhanced atomic layer deposition of three oxides, thereby breaking centrosymmetry at the nanoscale. We observe that the optical nonlinearity depends on the thickness variation of the three constituent materials, SiO ₂ , TiO ₂ , and Al ₂ O ₃ , ranging from tens of nanometers to the atomic scale, and where the thin films exhibit second-order susceptibility at their interfaces. Our findings reveal that the enhancement of nonlinear optical properties is strongly correlated with a high interface density and superior interface quality, where the interface second-order nonlinearity transitions to bulk-like second-harmonic generation. An effective bulk second-order susceptibility of χ zzz = 2.0 ± 0.2 pm/V at 1032 nm is achieved, comparable to some conventional monocrystalline nonlinear materials.

DOI:

10.1364/OME.590548External link

University Bibliography Jena:

fsu_mods_00036144External link

DOI:

10.1201/9781003528371-17External link

University Bibliography Jena:

fsu_mods_00036322External link

We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.

DOI:

10.1017/hpl.2025.10103External link

University Bibliography Jena:

fsu_mods_00035153External link

What we believe to be a new scalar and data-driven approach to experimentally characterize the transverse modes of optical fibers is proposed in this paper. It retrieves the orthogonal modal base set of the fiber via singular value decomposition after collecting a large set of data under different coupling conditions. The results show good agreement with the simulated transverse modes. Due to its operating principle, this approach can characterize any fiber, regardless of its length or size, a prominent advantage compared to other experimental approaches.

DOI:

10.1364/OE.583008External link

University Bibliography Jena:

fsu_mods_00035538External link

High harmonic generation (HHG) is a crucial technology for compact, high-brightness extreme ultraviolet (XUV) and soft X-ray sources, which are key to advancing both fundamental and applied sciences. The availability of advanced driving lasers, with tunable wavelength, power, and pulse duration, opens new opportunities for optimizing HHG-based sources. While scaling laws for driving wavelengths are well understood, this work focuses on how pulse duration impacts HHG efficiency and introduces a unified framework that links microscopic dynamics to macroscopic performance. We establish a practical scaling law for the single-atom dipole moment under phase-matching conditions, demonstrating a τ-1 dependence at 515 nm wavelength. By connecting this microscopic scaling to macroscopic conversion efficiency, we provide clear guidelines for optimizing HHG output across different gases and driving wavelengths. Furthermore, we identify fundamental constraints, including the carrier-envelope-phase (CEP) walk-off, which limits efficiency at longer driver wavelengths and becomes especially significant for very short pulses. All predictions are based on simple, accessible formulas, eliminating the need for complex numerical simulations. Experiments confirm these predictions and highlight when short pulses are advantageous, particularly in scenarios where CEP walk-off and absorption effects are minimized. These findings offer practical principles for designing next-generation HHG sources, capable of Watt-level average power and extended spectral reach, enabling more versatile and powerful HHG-based XUV and soft X-ray sources.

DOI:

10.1186/s43074-026-00249-zExternal link

University Bibliography Jena:

fsu_mods_00036364External link

DOI:

10.1016/j.yofte.2025.104471External link

University Bibliography Jena:

fsu_mods_00028951External link

It has been previously observed that each core in a multi-core fiber has its own birefringence properties. Therefore, obtaining a laser output with a well-defined polarization pattern from a multi-core fiber is challenging. In this work, we explain the origin of this core-dependent birefringence and present a polarization-maintaining, 35-core fiber design that is tested in an oscillator setup, delivering over 100W of power with a polarization contrast ratio close to 10dB. This is a significant improvement with respect to a comparable non-polarization-maintaining multi-core fiber.

DOI:

10.1364/OE.579763External link

University Bibliography Jena:

fsu_mods_00030211External link

This work presents the simultaneous scaling of the average power and pulse energy emitted by multicore fiber laser systems. This is achieved through two series of experiments that use a generation of Yb-doped multicore fiber amplifiers with 49 cores, seeded by a Q-switched multicore fiber laser. One of the main results of these experiments is a total pulse energy of up to 117 mJ at a repetition rate of 5 kHz in quasi-continuous pumping operation. In a different experiment with a smaller core size multicore fiber, an average power of 400 W was achieved at a repetition rate of 5 kHz, corresponding to a pulse energy of 80 mJ in continuous pumping. The experimental results match our simulation predictions, providing valuable insights into the further energy scalability of Yb-doped multicore fibers.

DOI:

10.1364/OE.579999External link

University Bibliography Jena:

fsu_mods_00030210External link