We investigated the adaptation and performance of Masked Autoencoders (MAEs) with Vision Transformer (ViT) architectures for self-supervised representation learning on one-dimensional (1D) ultrasound signals. Although MAEs have demonstrated significant success in computer vision and other domains, their use for 1D signal analysis, especially for raw ultrasound data, remains largely unexplored. Ultrasound signals are vital in industrial applications such as non-destructive testing (NDT) and structural health monitoring (SHM), where labeled data are often scarce and signal processing is highly task-specific. We propose an approach that leverages MAE to pre-train on unlabeled synthetic ultrasound signals, enabling the model to learn robust representations that enhance performance in downstream tasks, such as time-of-flight (ToF) classification. This study systematically investigated the impact of model size, patch size, and masking ratio on pre-training efficiency and downstream accuracy. Our results show that pre-trained models significantly outperform models trained from scratch and strong convolutional neural network (CNN) baselines optimized for the downstream task. Additionally, pre-training on synthetic data demonstrates superior transferability to real-world measured signals compared with training solely on limited real datasets. This study underscores the potential of MAEs for advancing ultrasound signal analysis through scalable, self-supervised learning.

Unlike robots, humans have no problem working hand in hand. However, when robots try to perform tasks that require precision, they always face a major problem: they are not precise enough in combination. This problem is especially relevant when the application requires high precision. One of the main reasons for this is that the robots usually do not know each other's position or have an absolute calibration of the common coordinate system with the required accuracy. We will present our approach to introduce precise alignment procedures in a robotic cell using optically assisted methods. Subsequent analysis of the acquired data by tailored optimization algorithms provide an accurate and absolute coordinate system for a robot ensemble. The accuracy is typically limited by the workspace environment. Mostly acoustic vibrations will define the lower limit of the absolute precision to retrieve a global coordinate system within the working environment. In this work we present an analysis of common limitations as well as an algorithmic procedure to retrieve a global orthonormal basis for the robotic workcell, independent of the number of robots in the ensemble. As an intermediate result of our ongoing research, we can demonstrate a repeatable adjustment accuracy of less than 100 mu m euclidean distance from a common center.

We present a pulse-preserving multilayer-based extreme-ultraviolet (XUV) monochromator providing ultra-narrow bandwidth (ΔE<0.6eV, Ec=92eV) and compact footprint (28×10cm2) for easy integration into high-harmonic generation (HHG) or free-electron laser (FEL) sources. The temporal resolution of the novel design supports pulse durations of typical pump–probe setups in the femtosecond and attosecond regime, depending on the mirror design and focusing geometries over the tuning range of the monochromator. The theoretical design is analyzed and experimentally characterized in a laser-driven HHG setup.

This study is focused on optimizing electromagnetic acoustic transducer (EMAT) sensors for enhanced ultrasonic guided wave signal generation in steel cables using CAD and modern manufacturing to enable contactless ultrasonic signal transmission and reception. A lab test rig with advanced measurement and data processing was set up to test the sensors’ ability to detect cable damage, like wire breaks and abrasion, while also examining the effect of potential disruptors such as rope soiling. Machine learning algorithms were applied to improve the damage detection accuracy, leading to significant advancements in magnetostrictive measurement methods and providing a new standard for future development in this area. The use of the Vision Transformer Masked Autoencoder Architecture (ViTMAE) and generative pre-training has shown that reliable damage detection is possible despite the considerable signal fluctuations caused by rope movement.

We present a versatile high repetition rate, optical-parametric chirped-pulse amplifier system (OPCPA) in combination with a high-harmonic-generation (HHG) source. Tuning of the fundamental OPCPA driver wavelength allows for high harmonic generation within the full range between 25 and 50 eV. All energies between two adjacent odd harmonics can be addressed, making the system a powerful, gaplessly tunable extreme-ultraviolet (XUV) light source for spectroscopy.

In this article we present a theoretical investigation of gold-silica-silver nanostructures and their optical properties with respect to ultrafast electronic applications and coherent control by tailored optical fields. We found a remarkable sensitive behavior to the carrier envelope phase (CEP) of the driving laser pulses in the coupling of surface and bulk plasmons leading to a superposition of distinct modes with a time-dependent amplitude structure. Furthermore, we show a rather complex temporal evolution of plasmonic surface modes. Our results suggest the potential for coherent control of the time-dependent resonant coupling between surface and volume modes by tailored laser pulses and foster the field of time-dependent spectroscopy of thinfilm hybrid nanostructures with single layer thickness down to the two-dimensional limit.

Minimizing the CEP jitter of isolated attosecond pulses (IAP) will be important for future applications. This jitter is experimentally and theoretically investigated and can be minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Thus, understanding and characterization of the CEP jitter of IAPs is a first step towards exact control of the electric field of IAP pulses.

We present a multilayer-mirror-based monochromator providing ultra-narrow bandwidth and compact footprint for easy integration into HHG-based or FEL sources. The bandwidth (ΔE<0.5eV, Ec=~91eV) of the monochromator is characterized experimentally in a HHG-based source.

The carrier envelope phase (CEP) jitter of isolated attosecond pulses (IAPs) produced by high harmonic generation (HHG) is theoretically investigated based on the assumption that a significant contribution originates from the measurable CEP jitter of the driving laser pulses. By solving the time-dependent Schrodinger equation, it is demonstrated that the attosecond CEP jitter of IAPs is minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Although at present the utilization of the CEP of IAPs has limited applications, understanding and characterization of the CEP jitter of IAPs is the first step toward exact control of the electric field of extreme ultraviolet pulses. (C) 2018 Optical Society of America

The carrier envelope phase (CEP) jitter of isolated attosecond pulses (IAPs) is theoretically and experimentally investigated based on the assumption that a significant contribution originates from the measurable CEP jitter of the driving laser. By solving the time-dependent Schrödinger equation, it is demonstrated that the attosecond CEP jitter of IAPs is minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Although, at present the utilization of the CEP of IAPs has limited applications, understanding and characterization of the CEP jitter of IAPs is the first step towards exact control of the electric field of extreme ultraviolet (XUV) pulses.

In this article we present a new diagnostic approach utilizing flow-cytometry to study compounds of nanoparticle samples in solution by analysis of their scattering patterns retrieved from the cytometric measurements. As a specific enhancement of this technique we study as well the scattering pattern of nanoparticles in a fluorescent solution (529 nm). A significant enhancement of the cytometry measurements is observed supporting an improved separation of particle formations that are clearly resolved in the cytograms. The samples in this experiment are prepared from 80 nm citrate-capped gold nanoparticles (AuNP). They are stabilized providing 2-(dimethylamino)ethanol (DMAE) in the aqueous solution. A laser diode with a wavelength of 488 nm is used as fundamental illumination for the flow-cytometry measurements (FCM). Dynamic Light Scattering (DLS) measurements are performed separately and demonstrate a very good agreement with the Flow-Cytometry measurements both of which allow to give an effective size calibration. For further analysis light transport simulations are presented. They provide information on the key-process to form the correlation of the fluorescent solutions FCM to the studied particles of interest. From this we extract the volume nature of the scattering process ensuring the correlation.

In this article we present a theoretical investigation of gold-silica-gold nanostructures and their properties depending on layer thickness and diameter. We found a remarkable sensitive behavior in the coupling of surface and bulk plasmons with respect to the outer geometry of the disk-like resonators leading to a superposition of distinct modes with a time-dependent amplitude structure. Furthermore, we show a rather complex temporal evolution of plasmonic surface modes depending on the top layer thickness and the asymmetry of the metal disk radii. The results suggest the coherent control of the time-dependent resonant coupling between surface and volume modes by adaptive pulse shaping and foster the field of time-dependent spectroscopy of thin film hybrid nanostructures with single layer thickness down to the two-dimensional limit.

The response of solids to electromagnetic fields is of crucial importance in many areas of science and technology. Many fundamental questions remain to be answered about the dynamics of the photoexcited electrons that underpin this response, which can evolve on timescales of tens to hundreds of attoseconds. How, for example, is the photoexcited electron affected by the periodic potential as it travels in the solid, and how do the other electrons respond in these strongly correlated systems? Furthermore, control of electronic motion in solids with attosecond precision would pave the way for the development of ultrafast optoelectronics. Attosecond electron dynamics can be traced using streaking, a technique in which a strong near-infrared laser field accelerates an attosecond electron wavepacket photoemitted by an extreme ultraviolet light pulse, imprinting timing information onto it. We present attosecond streaking measurements on the wide-bandgap semiconductor tungsten trioxide, and on gold, a metal used in many nanoplasmonic devices. Information about electronic motion in the solid is encoded on the temporal properties of the photoemitted electron wavepackets, which are consistent with a spread of electron transport times to the surface following photoexcitation. (C) 2015 Optical Society of America

We propose an experimental arrangement to image, with attosecond resolution, transient surface plasmonic excitations. The required modifications to state-of-the-art setups used for attosecond streaking experiments from solid surfaces only involve available technology. Buildup and lifetimes of surface plasmon polaritons can be extracted and local modulations of the exciting optical pulse can be diagnosed in situ.

In order to compute the spatial integral in Eq. (1), we consider a case where the bright and dark modes can both be excited at frequencies ωb and ωd, respectively. “Bright” and “dark” refer to the coupling properties of the modes: the bright mode couples efficiently with incident radiation, the dark poorly. The two frequencies are well separated. Each mode consists of two counterpropagating plasmons. In addition, we admit a term describing the ringing of localized modes excited in the focus of the NIR pulse (see, e.g., [1]). The contributions in each mode m = b, d are

Photoelectron studies in attoscience could be used to characterise plasmons excited in nanoparticles using few-cycle femtosecond pulses. We have used ion bombardment to sputter clean gold nanoparticles without significantly modifying their morphology.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text W. A. Okell, D. Fabris, M. Rahmani, Y. Sonnefraud, J. Hengster, D. Walke, D. Y. Lei, S. A. Maier, T. Uphues, T. Witting, J. P. Marangos, and J. W. G. Tisch, "Attosecond streaking on gold films," in Research in Optical Sciences , OSA Technical Digest (online) (Optica Publishing Group, 2014), paper HW4C.7. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Velocity-map imaging has been employed to study the photoemission in Ne and N(4,5)OO Auger decay in Xe induced by an isolated 85 eV extreme ultraviolet (XUV) pulse in the presence of a strong few-cycle near-infrared (NIR) laser field. Full three-dimensional momentum information about the released electrons was obtained. The NIR and XUV pulse parameters were extracted from the measured Ne streaking traces using a FROG CRAB retrieval algorithm. The attosecond measurements of the Auger decay in Xe show pronounced broadening of the Auger lines corresponding to the formation of sidebands. The temporal evolution of the sideband signals and their asymmetry along the laser polarization axis exhibit oscillations similar to those known from attosecond streaking measurements. The experimental results are in good agreement with model calculations based on an analytical solution of the Schrodinger equation within the strong field approximation.

Tracking and controlling electron dynamics in the interior of atoms, molecules as well as in solids is at the forefront of modern ultrafast science [1–5] . Time-resolved studies of these dynamics require attosecond temporal resolution that is provided by an ensemble of techniques consolidated under the term “attosecond metrology” [6,7] . This work reports the development and commissioning of what we refer to as next-generation attosecond beamline technology: the AS-1 attosecond beamline at the Max-Planck Institute of Quantum Optics. It consists of a phase-stabilized few-cycle laser system, for the generation of XUV radiation, and modules tailored for the spectral filtering and isolation of attosecond pulses as well as for their temporal characterization. The setup produces the shortest attosecond pulses demonstrated to date and combines them with advanced spectroscopic instrumentation (electron-, ion- and XUV-spectrometers). These pulses serve as temporally confined trigger events (attosecond streaking and tunneling spectroscopy) or probe pulses (attosecond absorption and photoelectron spectroscopy) enabling attosecond chronoscopy to be applied to a broad range of systems belonging to the microcosm.