Minimum Spot Size Research Articles

Fabrication of high-resolution, flexible, laser-induced graphene sensors via stencil masking

The advent of wearable sensing platforms capable of continuously monitoring physiological parameters indicative of health status have resulted in a paradigm shift for clinical medicine. The accessibility and adaptability of such portable, unobtrusive devices enables proactive, personalized care based on real-time physiological insights. While wearable sensing platforms exhibit powerful capabilities for continuously monitoring physiological parameters, device fabrication often requires specialized facilities and technical expertise, restricting deployment opportunities and innovation potential. The recent emergence of rapid prototyping approaches to sensor fabrication, such as laser-induced graphene (LIG), provides a pathway for circumventing these barriers through low-cost, scalable fabrication. However, inherent limitations in laser processing restrict the spatial resolution of LIG-based flexible electronic devices to the minimum laser spot size. For a CO2 laser–a commonly reported laser for device production–this corresponds to a feature size of ∼120 μm. Here, we demonstrate a facile, low-cost stencil-masking technique to reduce the minimum resolvable feature size of a LIG-based device from 120 ± 20 μm to 45 ± 3 μm when fabricated by CO2 laser. Characterization of device performance reveals this stencil-masked LIG (s-LIG) method yields a concomitant improvement in electrical properties, which we hypothesize is the result of changes in macrostructure of the patterned LIG. We showcase the performance of this fabrication method via production of common sensors including temperature and multi-electrode electrochemical sensors. We fabricate fine-line microarray electrodes not typically achievable via native CO2 laser processing, demonstrating the potential of the expanded design capabilities. Comparing microarray sensors made with and without the stencil to traditional macro LIG electrodes reveals the s-LIG sensors have significantly reduced capacitance for similar electroactive surface areas. Beyond improving sensor performance, the increased resolution enabled by this metal stencil technique expands capabilities for scalable fabrication of high-performance wearable sensors in low-resource settings without reliance on traditional fabrication pathways.

Optimization of synchrotron radiation parameters using swarm intelligence and evolutionary algorithms.

Alignment of each optical element at a synchrotron beamline takes days, even weeks, for each experiment costing valuable beam time. Evolutionary algorithms (EAs), efficient heuristic search methods based on Darwinian evolution, can be utilized for multi-objective optimization problems in different application areas. In this study, the flux and spot size of a synchrotron beam are optimized for two different experimental setups including optical elements such as lenses and mirrors. Calculations were carried out with the X-ray Tracer beamline simulator using swarm intelligence (SI) algorithms and for comparison the same setups were optimized with EAs. The EAs and SI algorithms used in this study for two different experimental setups are the Genetic Algorithm (GA), Non-dominated Sorting Genetic Algorithm II (NSGA-II), Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC). While one of the algorithms optimizes the lens position, the other focuses on optimizing the focal distances of Kirkpatrick-Baez mirrors. First, mono-objective evolutionary algorithms were used and the spot size or flux values checked separately. After comparison of mono-objective algorithms, the multi-objective evolutionary algorithm NSGA-II was run for both objectives - minimum spot size and maximum flux. Every algorithm configuration was run several times for Monte Carlo simulations since these processes generate random solutions and the simulator also produces solutions that are stochastic. The results show that the PSO algorithm gives the best values over all setups.

Optimization of Radiation Exposure when Examining Patients with Pathology of the Craniovertebral Region

The diagnostics are based on the principle of obtaining informative and high-quality images with minimal radiation exposure using radiation diagnostic methods: traditional radiography, multislice and cone-beam computed tomography.When conducting X-ray examinations, the main factors in reducing the risk of radiation exposure are the use of highly sensitive digital diagnostic image receivers, minimal exposure time, and a minimum number of images per examination. A lower current value and high anode voltage values, a minimum focal spot size, the placement of the tube as far as possible from the patient and the image receiver as close to the patient as possible, collimation of the radiation beam, and preference for a low radiation dose rate mode are also factors in reducing the risk of radiation exposure.Imaging of the craniovertebral region using cone beam computed tomography offers the opportunity to evaluate the bone structure of the region in detail, with an equal or less effective dose to the patient.

Development of sub-mirror radius of curvature automatic test system for IACT

The Image Air shower Cherenkov Telescope (IACT) is one powerful instrument to study gamma ray astronomy. Generally the reflection system of IACT is assembled by multiple small sub-mirrors. It is time-consuming and costly to measure the sub-mirrors for the traditional manual method. In order to solve the problem, we design and develop an automatic system to measure the radius of curvature (ROC) of spherical sub-mirrors. A foam aluminum sample spherical mirror is tested to verify system performance. The repeated measurement error of the system ROC is 5.68 mm with the step 5 mm, and the minimum spot size repeated measurement error is 0.04 mm. The results indicate that the accuracy and stability of the system are excellent. Two mirrors with different ROC are measured. The ROC of the aluminum foam structure mirror is 16100.30 ± 5.59 mm, and the minimum spot size is 3.37 ± 0.04 mm. The ROC of a glass mirror is 5810.00 ± 1.42 mm with the step 1 mm and a minimum spot size of 1.92 ± 0.02 mm. The results indicate that the system is suitable for measuring mirrors with different ROCs and the measurement results are effective and reliable. It is vital to note that the measurement is fast and unattended, the single measurement time is less than 5 minutes and the total time is less than 15 minutes.

Impact of wavelength and spot size on laser depth of focus: Considerations for mass spectrometry imaging of non‐flat samples By Alena N. Joignant, Ying Xi and David C. Muddiman

This month’s tutorial walks through the parameters that affect the laser ablation-based mass spectrometry imaging (MSI) of non-flat surfaces with the ambition of making MSI-relevant considerations more accessible to the broader community. Specifically, equations for the depth of focus and minimum spot size are related to the laser wavelength and beam quality in use. This tutorial explains the differences between ultraviolet and infrared laser MSI platforms in relation to these properties, as well as provides modern approaches in the field for the imaging of non-flat surfaces.

Self-focusing of a q-gaussian laser beam under the influence of an exponential plasma density ramp in plasma

The goal of the current manuscript is to investigate how a plasma density ramp affects the ability of a q-Gaussian laser beam (q-GLB) to self-focus in plasma. The laser beam exhibits oscillatory self-focusing and defocusing behaviour with increasing distance of propagation. We used an exponential plasma density ramp to combat this defocusing tendency, allowing the particular laser beam to achieve a minimal spot size and nearly retain it up to several Rayleigh lengths. In addition to that, it has been observed that self-focusing increases with increasing q-values and the laser intensity. However, the lower values of q suggest strong self-focusing. By warily selecting the plasma and laser parameters, the density ramp could play a key role in the self-focusing of q-Gaussian laser. Self-focusing is seen to become stronger as propagation distance increases and the q-parameter affects the behaviour of the beam-width parameter in the plasma as shown.

Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

Investigation of polycapillary half lenses for quantitative confocal micro-X-ray fluorescence analysis.

The use of polycapillary optics in confocal micro-X-ray fluorescence analysis (CMXRF) enables the destruction-free 3D investigation of the elemental composition of samples. The energy-dependent transmission properties, concerning intensity and spatial beam propagation of three polycapillary half lenses, which are vital for the quantitative interpretation of such CMXRF measurements, are investigated in a monochromatic confocal laboratory setup at the Atominstitut of TU Wien, and a synchrotron setup on the BAMline beamline at the BESSY II Synchrotron, Helmholtz-Zentrum-Berlin. The empirically established results, concerning the intensity of the transmitted beam, are compared with theoretical values calculated with the polycap software package and a newly presented analytical model for the transmission function. The resulting form of the newly modelled energy-dependent transmission function is shown to be in good agreement with Monte Carlo simulated results for the complete energy regime, as well as the empirically established results for the energy regime between 6 keV and 20 keV. An analysis of possible fabrication errors was conducted via pinhole scans showing only minor fabrication errors in two of the investigated polycapillary optics. The energy-dependent focal spot size of the primary polycapillary was investigated in the laboratory via the channel-wise evaluation of knife-edge scans. Experimental results are compared with data given by the manufacturer as well as geometric estimations for the minimal focal spot size. Again, the resulting measurement points show a trend in agreement with geometrically estimated results and manufacturer data.

Nanoscale Valley Modulation by Surface Plasmon Interference.

Excitons in two-dimensional (2D) materials have attracted the attention of the community to develop improved photoelectronic devices. Previous reports are based on direct excitation where the out-of-plane illumination projects a uniform single-mode light spot. However, because of the optical diffraction limit, the minimal spot size is a few micrometers, inhibiting the precise manipulation and control of excitons at the nanoscale level. Herein, we introduced the in-plane coherent surface plasmonic interference (SPI) field to excite and modulate excitons remotely. Compared to the out-of-plane light, a uniform in-plane SPI suggests a more compact spatial volume and an abundance of mode selections for a single or an array of device modulation. Our results not only build up a fundamental platform for operating and encoding the exciton states at the nanoscale level but also provide a new avenue toward all-optical integrated valleytronic chips for future quantum computation and information applications.

Different Approaches for Manufacturing Ti-6Al-4V Alloy with Triply Periodic Minimal Surface Sheet-Based Structures by Electron Beam Melting.

Targeting biomedical applications, Triply Periodic Minimal Surface (TPMS) gyroid sheet-based structures were successfully manufactured for the first time by Electron Beam Melting in two different production Themes, i.e., inputting a zero (Wafer Theme) and a 200 µm (Melt Theme) wall thickness. Initial assumption was that in both cases, EBM manufacturing should yield the structures with similar mechanical properties as in a Wafer-mode, as wall thickness is determined by the minimal beam spot size of ca 200 µm. Their surface morphology, geometry, and mechanical properties were investigated by means of electron microscopy (SEM), X-ray Computed Tomography (XCT), and uniaxial tests (both compression and tension). Application of different manufacturing Themes resulted in specimens with different wall thicknesses while quasi-elastic gradients for different Themes was found to be of 1.5 GPa, similar to the elastic modulus of human cortical bone tissue. The specific energy absorption at 50% strain was also similar for the two types of structures. Finite element simulations were also conducted to qualitatively analyze the deformation process and the stress distribution under mechanical load. Simulations demonstrated that in the elastic regime wall, regions oriented parallel to the load are primarily affected by deformation. We could conclude that gyroids manufactured in Wafer and Melt Themes are equally effective in mimicking mechanical properties of the bones.

Minimal Focal Spot Size Measured Based on Intensity and Power Flow.

It is shown, theoretically and numerically, that the distributions of the longitudinal energy flow for tightly focused light with circular and linear polarization are the same, and that the spot has circular symmetry. It is also shown that the longitudinal energy flows are equal for optical vortices with unit topological charge and with radial or azimuthal polarization. The focal spot has a minimum diameter (all other characteristics being equal), which is measured based on the intensity of an optical vortex with azimuthal polarization. The diameter of the focal spot calculated from the energy flow for light with circular or linear polarization is slightly larger (by a fraction of a percentage). The magnitude of the diameter based on the intensity plays a role in the interaction of light with matter, and the magnitude of the diameter based on the energy flux affects the resolution in optical microscopy which is crucial in sensorial applications.

Focusing properties and focal shift of a vortex cosine-hyperbolic Gaussian beam

In this paper, we investigate the focusing properties of a vortex-cosh-Gaussian (vChG) beam passing through a converging thin lens. Based on the Huygens–Fresnel diffraction integral, we derived the analytical propagation equation as well as the beam width expression of a focused vChGB. It is shown that the focusing properties including the focal shift of the focused vChGB are crucially dependent on the incident beam parameters namely the decentered parameter and the topological charge in addition to the Gaussian Fresnel number \(N_{F}\). From typical numerical examples, it is found that the focused vChGB is transformed into a multi-lobes structure shape at the real focus plane, and the principal maximum intensity of the beam is located away from the axis. The amount of focal shift, which is determined from the minimum spot size criterion, is strongly dependent on the Fresnel number, the decentered parameter and the vortex charge m. The obtained results may be useful for the applications of the vChGBs in beam shaping and beam focusing.

Beam optics in nuclear microprobe: A review

The beam optics in a nuclear microprobe is considered on the basis of quality criteria for focusing systems. In this consideration, empirical criteria with dominant chromatic or intrinsic spherical aberrations are used. In a more general criterion, where all aberrations can be taken into account, the maximum acceptance for a fixed beam spot size on the target is used. Another criterion, that is closest to an experiment, is based on the condition of the minimum spot size at a fixed beam current and takes into account the nonuniform distribution of ions in the phase volume. This review summarizes the studies of various types of quadrupole focusing systems and implies the need for further development of the nuclear microprobe by using aberration correctors and a compact system. The analysis of the influence of various aberrations on the resolution of a nuclear microprobe is conducted with special attention paid to the positioning aberrations in separated quadrupole probe-forming systems. It is demonstrated why integrated multiplets of quadrupole lenses are preferred in such systems. Methods to process experimental results for an adequate determination of the spot size on the target are considered.

Evaluation of a compact multicontrast and multiresolution X-ray phase contrast edge illumination system for small animal imaging.

In this work the performance of a compact multiresolution and multicontrast x-ray phase system based on edge illumination is investigated. It has been designed for small animal imaging and with a limited footprint for ease of deployment in laboratories. The presented edge illumination system is based on a compact microfocus tungsten x-ray source combined with a flat panel detector. The source has a maximum output of 10W when the minimum spot size of about 15μm is used. The system has an overall length of 70cm. A new double sample mask design, obtained by arranging both skipped and nonskipped configurations on the same structure, provides dual resolution capability. To test the system, we carried out computed tomography (CT) scans of a plastic phantom with different source settings using both single-image and multi-image acquisition schemes at different spatial resolutions. In addition, CT scans of an ex-vivo mouse specimen were acquired at the best identified working conditions to demonstrate the application of the presented system to small animal imaging. We found this system delivers good image quality, allowing for an efficient material separation and improving detail visibility in small animals thanks to the higher signal-to-noise ratio (SNR) of phase contrast with respect to conventional attenuation contrast. The system offers high versatility in terms of spatial resolution thanks to the double sample mask design integrated into a single scanner. The availability of both multi- and single-image acquisition schemes coupled with their dedicated retrieval algorithms, allows different working modes which can be selected based on user preference. Multi-image acquisition provides quantitative separation of the real and imaginary part of the refractive index, however, it requires a long scanning time. On the other hand, the single image approach delivers the best material separation and image quality at all the investigated source settings with a shorter scanning time but at the cost of quantitativeness. Finally, we also observed that the single image approach combined with a high-power x-ray source may result in a fast acquisition protocol compatible with in-vivo imaging.

Direct Lightning Initiation of HMX

HMX can be detonated by an exploding bridgewire (EBW) or a slapper. Direct HMX detonation by an electrical arc has not been demonstrated. This paper shows that the shock from a 99% worst-case lightning current (200 kA and 500 ns rise time) can detonate standard-density HMX at elevated temperatures (i.e., HMX in the most sensitive $$\delta$$ -phase at a temperature above 177°C) and that the shock from a 200-kA peak current pulse with a 100 ns rise time can detonate HMX at ambient temperatures. Two necessary detonation conditions are used for these assertions. The relevant Pop-Plot for HMX is converted into an empirical detonation criterion, which is applicable to explosives subject to shocks of variable pressure. The minimum detonation spot size for detonation reported in the literature is used as the other condition. PBX-9501 and LX-04 have similar Pop-Plots to those of HMX; thus, the HMX result is directly applicable. Although PBX-9404 and PBX-9407 are HMX-based, they have somewhat lower Pop-Plot pressures than HMX and are more sensitive to shocks caused by electrical arcs than HMX. As the HMX thermal conductivity is low and the phase transition can be slow, the chance of having a sufficient amount of HMX converted to $$\delta$$ -HMX during an accident is small; therefore, the threat of lightning shock-detonating HMX is very low. We recommend lightning simulation tests to be conducted for $$\delta$$ -HMX. We also would like to point out that a lightning can ignite HMX, which, in turn, leads to detonation via the deflagration-to-detonation transition.

Localized and Programmable Chemical Vapor Deposition Using an Electrically Charged and Guided Molecular Flux.

Chemical vapor deposition is a widely used material deposition technique. It commonly provides a uniform material flux to the substrate to cause uniform thin film growth. However, the ability to precisely adjust the local deposition rate would be highly preferable. This communication reports on a chemical vapor deposition method performed in a localized and programmable fashion by introducing an electrically charged and guided molecular flux. This allows for local adjustments of the deposition rate and three-dimensional shape by controlling the electric fields. Specifically, the precursor molecules are charged and then guided by arrays of electrodynamic funnels, which are created by a patterned dielectric layer, to predetermined deposition locations with a minimal spot size of 250 nm. Furthermore, nearest neighbor coupling is reported as a shaping method to cause the deposition of three-dimensional nanostructures. Additionally, the integration of individually addressable domain electrodes offers programmable charge dissipation to achieve an ON/OFF control. The described method is applicable to a wide variety of materials and precursors. Here, the localized and programmable deposition of three-dimensional copper oxide, chromium oxide, zinc oxide, and carbon nanowires is demonstrated.

High Spatial Resolution Optical Fiber Two Color Pyrometer With Fast Response

Among the different temperature measurement techniques providing micrometer resolution none of them provide fast response and easy access to close distances to the target surface in difficult to access areas. Optical fiber pyrometers provide that access but previous works used large optical fibers with numerical apertures limiting the minimum spot size to be measured. In this study, we propose a novel two colour optical fiber pyrometer based on a low diameter and numerical aperture optical fiber, low-noise photodetectors and high-gain transimpedance amplifiers with a high spatial resolution in the micrometre range and fast response. Using standard optical fibers and related devices provides also a low-cost system. The developed pyrometer presents a high spatial resolution of 16 μm for a target surface at 25 μm with a wide temperature range of 300 to 1200°C it being the highest spatial resolution for this kind of temperature systems. Theoretical analysis and measurements for different pyrometer configurations are reported. This study will help further the microthermography applications in machining processes.

Spatial resolution limits of EPMA

The development of field emission EPMA, has significantly improved the lateral resolution of EPMA. Two strategies are available for achieving high spatial resolution, either low overvoltage or low voltage analysis. Determining the spatial resolution for a particular analysis is complex and depends on the voltage, spot size, beam current, density of the sample, X-rays analysed and the precision and sensitivity required. Monte carlo simulations can be used to evaluate the spatial resolution for different analytical conditions and samples, provided the minimum spot size achievable at the conditions is known. Spot size is important in determining lateral resolution, which initially improves with decreasing accelerating voltages, and then increases as the minimum spot size becomes more significant than the distance electrons travel. For trace elements, the requirement for precision and sensitivity demands either higher overvoltages increasing the volume from which X-rays are generated, and/or higher beam currents increasing the spot size. At low overvoltage or low voltage conditions many additional factors must be considered: carbon contamination, coat thickness, erosion of the carbon coat, the stability of the sample and the problems surrounding the measurement of soft X-ray lines including L-lines for first row transition metals. When analysing L-lines for quantifying first row transition metals, either calibration curves must be used, or the anomalous mass absorption and variations in the fluorescence yields from partial shell occupancy must be accounted for, by using fits to experimentally determined values. By taking these factors into consideration, high quality measurements can be performed.

Phase-contrast x-ray tomography of neuronal tissue at laboratory sources with submicron resolution.

.Purpose: Recently, progress has been achieved in implementing phase-contrast tomography of soft biological tissues at laboratory sources. This opens up opportunities for three-dimensional (3-D) histology based on x-ray computed tomography (- and nanoCT) in the direct vicinity of hospitals and biomedical research institutions. Combining advanced x-ray generation and detection techniques with phase reconstruction algorithms, 3-D histology can be obtained even of unstained tissue of the central nervous system, as shown, for example, for biopsies and autopsies of human cerebellum. Depending on the setup, i.e., source, detector, and geometric parameters, laboratory-based tomography can be implemented at very different sizes and length scales.We investigate the extent to which 3-D histology of neuronal tissue can exploit the cone-beam geometry at high magnification using a nanofocus transmission x-ray tube (nanotube) with a 300 nm minimal spot size (Excillum), combined with a single-photon counting camera. Tightly approaching the source spot with the biopsy punch, we achieve high , high flux density, and exploit the superior efficiency of this detector technology.Approach: Different nanotube configurations such as spot size and flux, , as well as exposure time, Fresnel number, and coherence are varied and selected in view of resolution, field of view, and/or phase-contrast requirements.Results: The data show that the information content for the cytoarchitecture is enhanced by the phase effect. Comparison of results to those obtained at a microfocus rotating-anode x-ray tomography setup with a high-resolution detector, i.e., in low- geometry, reveals similar to slightly superior data quality for the nanotube setup. In addition to its compactness, reduced power consumption by a factor of , and shorter scan duration, the particular advantage of the nanotube setup also lies in its suitability for pixel detector technology, enabling an increased range of opportunities for applications in laboratory phase-contrast x-ray tomography.Conclusions: The phase retrieval scheme utilized mixes amplitude and phase contrast, with results being robust with respect to reconstruction parameters. Structural information content is comparable to slightly superior to previous results achieved with a microfocus rotating-anode setup but can be obtained in shorter scan time. Beyond advantages as compactness, lowered power consumption, and flexibility, the nanotube setup’s scalability in view of the progress in pixel detector technology is particularly beneficial. Further progress is thus likely to bring 3-D virtual histology to the performance in scan time and throughput required for clinical practice in neuropathology.

Phosphor material dependent spot size limitations in laser lighting.

In laser lighting, a major benefit over other lighting techniques is the possibility to achieve very high luminous exitance. Focusing the exciting laser to a very small spot size on the phosphor, however, does not necessarily provide a very small emitting area for the white light. In this study we investigate experimentally and numerically the relationship between the white light spot size and the incident blue laser spot size. We show that the specific phosphor material properties have significant impact on this relationship and on the achievable minimum spot size. This constitutes a limitation on the minimum spot size achievable in laser lighting and has important implications in applications.