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A localized energy deposition in a thin layer of liquid between two solid glass plates excites waves in the liquid, solids, and their interfaces. Of particular interest is an elastic surface wave (Rayleigh wave) on the liquid–solid interface that travels faster than the shock wave in the liquid. The surface deformation caused by the Rayleigh wave expands the layer of liquid, thereby locally reducing the pressure below the cavitation threshold. The created tension nucleates many cavitation bubbles, which later collapse due to the passage of the trailing shock wave in the liquid. Interestingly, the bubbles are not arranged homogeneously but on concentric rings centered on the location of the energy deposition. We explain the formation of the concentric rings with the interaction between neighboring bubbles. The fluid–structure interaction is modeled with a coupled finite volume solver that couples a multi-phase compressible fluid region (water and bubble gas) with an elastic solid (glass). We find that the nucleation of bubbles in such a geometry relaxes the tension in their immediate vicinity and thereby suppresses the growth of neighboring bubble nuclei. This idea is confirmed by a Rayleigh–Plesset model of a bubble driven by a far-field pressure obtained from the finite volume simulation. The observed ring patterns are thus the result of the successive activation of statistically distributed nucleation sites into explosively expanding cavitation bubbles in an axisymmetric geometry, whose strong interaction on short distances leads to a hindrance of bubble growth in radially distinct regions.

Superfluorescence (SF) in lanthanide doped upconversion nanoparticles (UCNPs) is a room-temperature quantum phenomenon, first discovered in 2022. In a SF process, the many emissive lanthanide ions within a single UCNP are coherently coupled by an ultra-short (ns or fs) high-power excitation laser pulse. This leads to a superposition of excited emissive states which decrease the emissive lifetime of the UCNP by a factor proportional to the square of the number of lanthanide ions which are coherently coupled. This results in a dramatic decrease in UCNP emission lifetime from the μs regime to the ns regime. Thus SF offers a tantalizing prospect to achieving superior upconversion photon flux in upconversion materials, with potential applications such as imaging and sensing. This perspective article contextualizes how SF-UCNPs can be regarded as a second generation quantum technology, and notes several challenges, opportunities, and open questions for the development of SF-UCNPs.

Photoacoustic tomography (PAT) has the potential to become a widely used imaging tool in preclinical studies of small animals. This is because it can provide non-invasive, label free images of whole-body mouse anatomy, in a manner which is challenging for more established imaging modalities. However, existing PAT scanners are limited because they either do not implement a full 3-D tomographic reconstruction using all the recorded photoacoustic (PA) data and/or do not record the available 3-D PA time-series data around the mouse with sufficiently high spatial resolution ( ∼100μ m), which compromises image quality in terms of resolution, imaging depth and the introduction of artefacts. In this study, we address these limitations by demonstrating an all-optical, multi-view Fabry-Perot based scanner for whole body small animal imaging. The scanner densely samples the acoustic field with a large number of detection points (>100,000), evenly distributed around the mouse. The locations of the detection points were registered onto a common coordinate system, before a tomographic reconstruction using all the recorded PA time series was implemented. This enabled the acquisition of high resolution, whole-body PAT images of ex-vivo mice, with anatomical features visible across the entire cross section.

The clinical assessment of microvascular pathologies (in diabetes and in inflammatory skin diseases, for example) requires the visualization of superficial vascular anatomy. Photoacoustic tomography (PAT) scanners based on an all-optical Fabry–Perot ultrasound sensor can provide highly detailed 3D microvascular images, but minutes-long acquisition times have precluded their clinical use. Here we show that scan times can be reduced to a few seconds and even hundreds of milliseconds by parallelizing the optical architecture of the sensor readout, by using excitation lasers with high pulse-repetition frequencies and by exploiting compressed sensing. A PAT scanner with such fast acquisition minimizes motion-related artefacts and allows for the volumetric visualization of individual arterioles, venules, venous valves and millimetre-scale arteries and veins to depths approaching 15 mm, as well as for dynamic 3D images of time-varying tissue perfusion and other haemodynamic events. In exploratory case studies, we used the scanner to visualize and quantify microvascular changes associated with peripheral vascular disease, skin inflammation and rheumatoid arthritis. Fast all-optical PAT may prove useful in cardiovascular medicine, oncology, dermatology and rheumatology.

We reveal for the first time by experiments that within a narrow parameter regime, two cavitation bubbles with identical energy generated in anti-phase develop a supersonic jet. High-resolution numerical simulation shows a mechanism for jet amplification based on toroidal shock wave and bubble necking interaction. The micro-jet reaches velocities in excess of 1000 m/s. We demonstrate that potential flow approximation established for Worthington jets accurately predicts the evolution of the bubble gas-liquid interfaces.

Photoacoustic imaging offers high spatial resolution, imaging depth, and molecular information, emerging as a promising biomedical imaging modality. In particular, when using exogenous contrast, the advantages of photoacoustic imaging can be more effectively utilized in preclinical and clinical studies. We provide a novel approach to screen and identify efficient photoacoustic performance as contrast agents of the metals. To accomplish this, we introduce a novel figure of merit that quantifies the potential performance of contrast agents. As a result of the quantification, we discover that Ti nanodiscs outperform Pt nanodiscs in terms of photoacoustic ability, which shows a similar level to Au nanodiscs. We compare these results by performing a photoacoustic phantom imaging experiment. The photoacoustic performance of the three materials is compared by comparing the signal intensity of the materials measured on the photoacoustic image for various wavelengths. The imaging results further support our findings, demonstrating the superior performance of Ti nanodiscs as contrast agents.

The growing demand for flexible, high-quality fabrication of free-form micro-optics drives the development of laser-based fabrication techniques for both the shape formation and surface polishing of optical elements. In this paper, we performed a thorough and systematic study on fused silica glass ablation using 10 ps and 320 fs duration pulses. Ablation processes for both pulse durations were optimized based on the measurements of the removed material layer thickness and surface roughness, and by analyzing the topographies of ablated cavities to remove material layers as thin as possible with minimum surface damage. Our findings demonstrate higher process resolution and surface quality for femtosecond pulses. Ablation of pre-roughened glass reduced the minimal removable glass layer thickness well below the 1 μm mark for both pulse durations, improving the process resolution. The minimal removable glass layer thickness was 14 times smaller for the femtosecond pulses, with up to 4.5 times lower surface roughness compared to samples processed with picosecond pulses. On the other hand, results revealed faster glass removal rates with picosecond pulses. In the end, arrays of microlenses were fabricated with both pulse durations and subsequently polished with a CO2 laser. Results revealed higher performance of microlenses fabricated with femtosecond pulses, providing better focusing capabilities and lesser beam scattering. Finally, this study demonstrated the successful fabrication of free-form optical elements with femtosecond and picosecond pulses, demonstrating the versatility and the potential of laser-based techniques.

Photonic-based methods are crucial in biology and medicine due to their non-invasive nature, allowing remote measurements without affecting biological specimens. The study of diatoms using advanced photonic methods remains a relatively underexplored area, presenting significant opportunities for pioneering discoveries. This research provides a comprehensive analysis of marine diatoms, specifically Nitzschia sp., across varying salinity levels, integrating fluorescence lifetime imaging microscopy (FLIM), combined photoacoustic and fluorescence tomographies (PAFT), and ultrastructural examinations using transmission electron microscopy. Key findings include a systematic shift in the mean fluorescence lifetime from 570 ps at 20‰ to 940 ps at 80‰, indicating functional adaptations in chlorophyll molecules within light-harvesting complexes. At 60‰ salinity, anomalies are observed in the development of silica valves and polysaccharide layers, suggesting abnormalities in valve morphogenesis. Lipid droplets within the cells display a minimum diameter at 40‰, indicating metabolic adjustments to osmotic stress. The intensity of both fluorescence and photoacoustic signals increases with increasing salinity levels. These insights enhance understanding of the ecological implications of salinity stress on diatom communities and pave the way for future research on leveraging the unique adaptive mechanisms of microalgae for environmental monitoring and sustainable biotechnological applications.

The flow around a bubble, precipitously expanding in a thin gap between flat walls, was found to have a peculiar feature: distinct fingering occurs at the bubble wall, which was observed through the ultra-high speed optical visualization. The effect is attributed to the reversal of the flow within boundary layers, which provokes the growth of instabilities at the inflection point and, when the surface tension is low enough (the local Weber number is high enough), leads to the fingering. In this paper, we show the high speed recordings of the fingering and model the evolution of the radial velocity to quantitatively confirm feasibility of the proposed instability mechanism.

Advancements in light engineering have led to the creation of pulsed laser sources capable of delivering high-repetition-rate, high-power few-cycle laser pulses across a wide spectral range, enabling exploration of many fascinating nonlinear processes occurring in all states of matter. High-harmonic generation, one such process, which converts the low-frequency photons of the driver laser field into soft x-rays, has revolutionized atomic, molecular, and optical physics, leading to progress in attosecond science and ultrafast optoelectronics. The Extreme Light Infrastructure, Attosecond Light Pulse Source (ELI ALPS) facility pioneers state-of-the-art tools for research in these areas. This paper outlines the design rationale, capabilities, and applications of plasma- and gas-based high-repetition-rate (1 kHz to 100 kHz) attosecond extreme ultraviolet (XUV) beamlines developed at ELI ALPS, highlighting their potential for advancing various research fields.