Scanning Regime Research Articles

Label-free image scanning microscopy for kHz super-resolution imaging and single particle tracking.

We report the modification of a label-free image scanning microscope (ISM) to perform asynchronous 2D imaging at up to 24kHz while keeping the lateral resolution gain and background rejection of a regular label-free ISM setup. Our method uses a resonant mirror oscillating at 12kHz for one-direction scanning and a chromatic line for instantaneous scanning in the other direction. We adapt optical photon reassignment in this scanning regime to perform fully optical super-resolution imaging. We exploit the kHz imaging capabilities of this confocal imaging system for single nanoparticle tracking down to 20 nm for gold and 50 nm for silica particles as well as imaging freely moving Lactobacillus with improved resolution.

Modeling of nanoparticle-sensitized spatially localized dynamic photohyperthermia in a blood vessel under infrared laser irradiation with a scanning beam

Photoheating in a venous blood vessel under near-infrared laser irradiation by a scanning laser beam, which is synchronized with the blood flow velocity, is analyzed numerically by considering the light scattering, absorption, and heat transfer in the blood and surrounding tissues. The scanning regime of the laser irradiation with a wavelength of 1064 nm is found to increase strongly the photoheating of the blood while minimizing the overheating of the skin and the tissues surrounding the blood vessel. Simulations show that the photoheating effect can be additionally enhanced by light-absorbing nanoparticles in the blood. The proposed approach of dynamic laser photohyperthermia with the scanning laser beam is discussed for potential applications in laser phototherapy.

Effects of Wave-Induced Doppler Velocity on the Sea Surface Current Measurements by Ka-Band Real-Aperture Radar with Small Incidence Angle

The Doppler shift of microwave radar sea surface echoes serves as the foundation for sea surface current field retrieval; it includes the shift caused by satellite platform motion, ocean waves, and sea surface currents. The Doppler shift caused by ocean waves is known as the wave-induced Doppler velocity (UWD), and its removal is critical for the accurate retrieval of sea surface current fields. The low-incidence Ka-band real-aperture radar rotary scan regime has the capability of directly observing wide-swath two-dimensional current fields, but as a new regime to be further explored and validated, simulation and analysis of UWD in this regime have a significant influence on the hardware design and currently observed applications of this satellite system in its conceptual stage. In this study, we simulated and investigated the impacts of radar parameters and sea-state conditions on the UWD obtained from small-incidence-angle Ka-band rotational scanning radar data and verified the simulation results with the classical analytical solution of average specular scattering point velocity. Simulation results indicate that the change in the azimuth direction of platform observation affects UWD accuracy. Accuracy is the lowest when the antenna is in a vertical side-view. The UWD increases slowly with the incidence angle. Ocean waves are insensitive to polarization in the case of small-incidence-angle specular scattering. The increase in wind speed and the development of wind waves result in a substantial increase in UWD. We classified swell by wavelength and wave height and found that UWD increases with swell size, especially the contribution of swell height to UWD, which is more significant. The contribution of the swell to UWD is smaller than that of wind waves to UWD. Furthermore, the existence of sea surface currents changes the contribution of ocean waves to UWD, and the contribution weakens with increasing wind speed and increases with wind wave development.

Processes of ablation and structures growth under the action of femtosecond laser pulses on the gallium surface in an ammonia medium

In this paper, we present the results of processing metallic gallium in an ammonia vapor medium at 2 bar pressure by femtosecond laser pulses. The influence of the ammonia concentration and the mode of laser beam scanning on the result of laser action is considered. It has been established that an increase in the concentration of ammonia vapor and a change in the scanning regime lead to a radical change in the laser ablation process. A decrease in the scanning speed leads to the cessation of the ablation process and the development of the nitridation process of the gallium surface, accompanied by the formation of columnar structures up to 12 mm long and about 100 μm in diameter. The synthesized nanoparticles and structures were studied using scanning electron microscopy, Raman spectroscopy, and X-ray analysis. Keywords: laser ablation, gallium nitride, gallium nitride nanoparticles manufacturing, ablative synthesis of gallium nitride nanoparticles.

Процессы абляции и роста структур при воздействии фемтосекундных лазерных импульсов на поверхность галлия в среде аммиака

In this paper, we present the results of processing metallic gallium in an ammonia vapor medium at 2 bar pressure by femtosecond laser pulses. The influence of the ammonia concentration and the mode of laser beam scanning on the result of laser action is considered. It has been established that an increase in the concentration of ammonia vapor and a change in the scanning regime lead to a radical change in the laser ablation process. A decrease in the scanning speed leads to the cessation of the ablation process and the development of the nitridation process of the gallium surface, accompanied by the formation of columnar structures up to 12 mm long and about 100 μm in diameter. The synthesized nanoparticles and structures were studied using scanning electron microscopy, Raman spectroscopy, and X-ray analysis.

Waveguide Slot Array with Wide Frequency Scanning

A linear waveguide slot antenna with a frequency scanning sector of 180° is proposed and studied. The antenna represents a rectangular metal waveguide filled with a two-layer dielectric with periodic steps of thickness in one layer and periodic triple transverse slots in the wide wall of the waveguide. A scanning sector of 180° is reached with the aid of two scanning regimes that employ the fundamental (zero) and minus first spatial harmonics. Such a waveguide slot antenna is characterized by a high antenna aperture efficiency in almost entire frequency scanning sector.

The influence of low-frequency magnetic field regions on the Saccharomyces cerevisiae respiration and growth

The influence of four low-frequency magnetic field (MF) ranges 10–300 Hz, 10–100 Hz, 10–50 Hz and 50–100 Hz in scanning regime (all frequencies from selected range were scanned during 100 s repetitively during 24 h) on baker’s yeast cells Saccharomyces cerevisiae was examined by continuous measurements of cumulative O2 consumption and cumulative CO2 production over 24 h with Micro-Oxymax® respirometer. Besides respiration activity, measurements of cell growth and glucose uptake were performed as well. Statistical analysis indicated that, among all investigated low-frequency MF ranges, range from 10 Hz to 50 Hz had the greatest influence to yeast cell respiration and cell growth. More precisely, for this region, paired two sample one-tail t-test showed statistically significant differences in cumulative O2 consumption, cumulative CO2 production and S. cerevisiae cell number. Moreover samples exposed to MF range from 10 Hz to 50 Hz showed the same behavior in all five replicates: lower cumulative O2 consumption, higher cumulative CO2 production and higher cell number compared to control sample. This could be important from the application aspect, in industry (food, feed, brewery etc.) and biotechnology, because changes in cells metabolism are not caused by chemical treatment.

Solidification pattern, microstructure and texture development in Laser Powder Bed Fusion (LPBF) of Al10SiMg alloy

A comprehensive analysis of solidification patterns and microstructural development is presented for an Al10SiMg sample produced by Laser Powder Bed Fusion (LPBF). Utilizing a novel scanning strategy that involves counter-clockwise rotation of the scan vector by 67° upon completion of each layer, a relatively randomized cusp-like pattern of protruding/overlapping scan tracks has been produced along the build direction. We show that such a distribution of scan tracks, as well as enhancing densification during LPBF, reduces the overall crystallographic texture in the sample, as opposed to those normally achieved by commonly-used bidirectional or island-based scanning regimes with 90° rotation. It is shown that, under directional solidification conditions present in LPBF, the grain structure is strictly columnar throughout the sample and that the grains' orientation aligns well with that of the α-Al cells. The size evolution of cells and grains within the melt pools, however, is shown to follow opposite patterns. The cells'/grains' size distribution and texture in the sample are explained via use of analytical models of cellular solidification as well as the overall heat flow direction and local solidification conditions in relation to the LPBF processing conditions. Such a knowledge of the mechanisms upon which microstructural features evolve throughout a complex solidification process is critical for process optimization and control of mechanical properties in LPBF.

Angular-Dependent Radius Measurements at Rotating Objects Using Underdetermined Sensor Systems

Precise and contactless shape measurements of rotating objects is important, e.g., for monitoring and controlling the manufacturing quality in lathes. For this purpose, multisensor and single-sensor approaches based on optical distance and surface velocity measurements are state-of-the-art techniques. Two- and single-sensor systems are particularly promising to measure the angular-dependent radius of the cross section of the rotating object in a scanning regime with minimal optical access. Since a comparison between the different sensor systems is missing, the potential of these underdetermined sensor systems is unclear. In addition, displacements of the rotational axis and sensor misalignments are suspected to be crucial error sources, but the error is unknown. For this reason, an error analysis is performed regarding the resulting systematic error and the random error for the two- and single-sensor systems. As a result, the different sensor systems have an equal cross-sensitivity with respect to lateral displacements of the rotational axis from the sensor axes, but the two-sensor approach has the lowest sensitivity regarding sensor misalignments. For the studied measurement conditions, the systematic error dominates the sensor noise for the two-sensor system and the single-sensor system with combined distance and velocity measurement at an object mean radius >6 mm. The smallest total measurement uncertainty is obtained with the two-sensor system. Finally, the relevance of systematic error depends on the utilization, i.e., for instance on the absolute rotor radius, the stability of the rotor axis, the sensor position, the accuracy of the sensor alignment, and the uncertainty of the distance and/or velocity measurements.

Многоосная гониометрическая 3D-визуализация векторных диаграмм оптических характеристик коллоидных и биологических структур на чипе на различных траекториях и режимах лазерного сканирования

Многоосная гониометрическая 3D-визуализация векторных диаграмм оптических характеристик коллоидных и биологических структур на чипе на различных траекториях и режимах лазерного сканирования

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is >1.5 carbon weight % (standard deviation ± 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Nanoscale Electrocatalysis of Hydrazine Electro-Oxidation at Blistered Graphite Electrodes.

There is great interest in finding and developing new, efficient, and more active electrocatalytic materials. Surface modification of highly oriented pyrolytic graphite, through the introduction of surface "blisters", is demonstrated to result in an electrode material with greatly enhanced electrochemical activity. The increased electrochemical activity of these blisters, which are produced by electro-oxidation in HClO4, is revealed through the use of scanning electrochemical cell microscopy (SECCM), coupled with complementary techniques (optical microscopy, field emission-scanning electron microscopy, Raman spectroscopy, and atomic force microscopy). The use of a linear sweep voltammetry (LSV)-SECCM scan regime allows for dynamic electrochemical mapping, where a voltammogram is produced at each pixel, from which movies consisting of spatial electrochemical currents, at a series of applied potentials, are produced. The measurements reveal significantly enhanced electrocatalytic activity at blisters when compared to the basal planes, with a significant cathodic shift in the onset potential of the hydrazine electro-oxidation reaction. The improved electrochemical activity of the hollow structure of blistered graphite could be explained by the increased adsorption of protonated hydrazine at oxygenated defect sites, the ease of ion-solvent intercalation/deintercalation, and the reduced susceptibility to N2 nanobubble attachment (as a product of the reaction). This study highlights the capability of electrochemistry to tailor the surface structure of graphite and presents a new electrocatalyst for hydrazine electro-oxidation.

Hydrogen diffusion in steels under electron bombardment

We report on the results of measurement of the coefficients of hydrogen diffusion through metal membranes in the course of their simultaneous hydrogen saturation and bombardment with electrons (energy 30 keV, current density from 3 to 30 µA/cm2) both in a broad and in a narrow beam. It is found that the time of hydrogen discharge from the membrane is determined by the parameters of the electron beam, its periodicity and duration, and also depends on the structure of the phase state of the metal membrane. It is shown that the diffusion coefficient increases when a narrow electron beam in the scanning regime is used. Analysis of the hydrogen yield as a function of time is carried out on a mass spectrometer connected to a vacuum chamber containing an electron gun, a beam sweep oscillator, and an electrolytic cell. The hydrogen diffusion coefficients under the action of a scanning electron beam are 15 times larger than under the same conditions without irradiation.

Laser ablation of single-crystalline silicon by radiation of pulsed frequency-selective fiber laser

We have studied the process of destruction of the surface of a single-crystalline silicon wafer scanned by the beam of a pulsed ytterbium-doped fiber laser radiation with a wavelength of λ = 1062 nm. It is established that the laser ablation can proceed without melting of silicon and the formation of a plasma plume. Under certain parameters of the process (radiation power, beam scan velocity, and beam overlap density), pronounced oxidation of silicon microparticles with the formation of a characteristic loose layer of fine powdered silicon dioxide has been observed for the first time. The range of lasing and beam scanning regimes in which the growth of SiO2 layer takes place is determined.

Continuous scanning mode for ptychography.

We outline how ptychographic imaging can be performed without the need for discrete scan positions. Through an idealized experiment, we demonstrate how a discrete-position scan regime can be replaced with a continuously scanned one with suitable modification of the reconstruction scheme based on coherent modes. The impact of this is that acquisition times can be reduced, significantly aiding ptychographic imaging with x rays, electrons, or visible light.

Capability of Flyuorat-02-Panorama spectrofluorimeter to analyze fluorescent dye mixtures

The excitation and emission spectra of dyes that could be used for indicator studies in the process of oilfield development (uranine, eosin Y, rhodamine B, rhodamine 6G, amino-G-acid) are investigated using a Flyuorat-02-Panorama spectrofluorimeter at different scanning regimes and at different pH values. Optimal conditions are elucidated for simultaneous separate determination: aqueous solution with pH 9.18 (borate buffer solution), λex = 300 nm (5 dyes) or 490 nm (4 dyes) with fluorescence spectra recording (registration scanning regime with spectrum cutoff in the region 480–580 or 500–600 nm, respectively); λex = 300 nm and Δλ = 25 nm with spectra recording in the range 300–680 nm using a regime of synchronous scanning (4 dyes). An algorithm is suggested for processing of spectra recorded using different methods. Dye concentrations in the mixture are calculated using the Panorama Pro, Version 2.1.0 software supplied with the instrument. The possibility of simultaneous separate determination of 2–5 dyes in the mixture was demonstrated.

Beam spatial profile effect on femtosecond laser surface structuring of titanium in scanning regime

We have developed a new method for manipulating nanotopology and chemical composition of titanium surfaces by a scanning femtosecond laser beam with an asymmetrical spatial fluence distribution. Using of a common Gaussian laser beam leads to formation of combined nano- and micro-scale surface topologies owing to superimposition of different laser beam parts during the surface scanning. In contrast, beam shaping results in presumable surface structuring at specific laser fluences yielding in “clean” surface structures. In a simple case, cutting of a half beam perpendicular to the scanning direction enables to eliminate surface nanotopology, leaving less oxidized, cleaner and smoother microspikes, just by changing the scanning direction. Optimal experimental conditions were revealed to obtain in air the topologically and chemically different surface structures using the asymmetrical femtosecond laser beam and the opposite scanning directions.

Formation of Porous Structure with Subspot Size under the Irradiation of Picosecond Laser Pulses

A study was presented in this paper on porous structure with microsize holes significantly smaller than laser spot on the stainless steel 304 target surface induced by a picosecond Nd:van regenerative amplified laser, operating at 1064 nm. The target surface variations were studied in air ambience. The estimated surface damage threshold was 0.15 J/cm2. The target specific surface changes and phenomena observed supported a complementary study on the formation and growth of the subspot size pit holes on metal surface with dependence of laser pulse number of 50–1000 and fluences of 0.8 and 1.6 J/cm2. Two kinds of porous structures were presented: periodic holes are formed from Coulomb Explosion during locally spatial modulated ablation, and random holes are formed from the burst of bubbles in overheated liquid during phase explosion. It can be concluded that it is effective to fabricate a large metal surface area of porous structure by laser scanning regime. Generally, it is also difficult for ultrashort laser to fabricate the microporous structures compared with traditional methods. These porous structures potentially have a number of important applications in nanotechnology, industry, nuclear complex, and so forth.

X-band rapid-scan EPR of nitroxyl radicals

X-band rapid-scan EPR spectra were obtained for dilute aqueous solutions of nitroxyl radicals 15N-mHCTPO (4-hydro-3-carbamoyl-2,2,5,5-tetra-perdeuteromethyl-pyrrolin-1- 15N-oxyl-d 12) and 15N-PDT (4-oxo-2,2,6,6-tetra-perdeuteromethyl-piperidinyl- 15N-oxyl-d 16). Simulations of spectra for 15N-mHCTPO and 15N-PDT agreed well with the experimental spectra. As the scan rate is increased in the rapid scan regime, the region in which signal amplitude increases linearly with B 1 extends to higher power and the maximum signal amplitude increases. In the rapid scan regime, the signal-to-noise for rapid-scan spectra was about a factor of 2 higher than for unbroadened CW EPR, even when the rapid scan spectra were obtained in a mode that had only 4% duty cycle for data acquisition. Further improvement in signal-to-noise per unit time is expected for higher duty cycles. Rapid scan spectra have higher bandwidth than CW spectra and therefore require higher detection bandwidths at faster scan rates. However, when the scan rate is increased by increasing the scan frequency, the increase in noise from the detection bandwidth is compensated by the decrease in noise due to increased number of averages per unit time. Because of the higher signal bandwidth, lower resonator Q is needed for rapid scan than for CW, so the rapid scan method is advantageous for lossy samples that inherently lower resonator Q.

Age and dose-limited PET-CT scan regime in lymphoma: between the devil and the deep blue sea?

In this study the authors speculate about hypothetical effective-dose (E) reduction through limiting post-chemotherapy PET-CT scanning to lymphoma sites previously identified on pre-treatment CT. E reductions/scan time savings are compared between post-treatment standard and theoretically limited PET-CT scans. The influence of patient age with E savings and associated clinical implication for 100 subjects are discussed. The greatest E theoretical savings of 52 and 32% for the CT contribution and combined PET-CT, respectively, were seen in patients <18 y old using limited scans in this study, with a potential mean time saving of 16 min per patient across the entire cohort. However, the limited PET-CT regime here missed a 1% rate of unexpected cancer that standard PET-CT recorded. The authors recommend performing larger scale multi-centre studies comparing PET-CT pre- and post-chemotherapy to establish full clinical efficacy of this method.