Grating Size Research Articles

Model of self-generated magnetic field generation from relativistic laser interaction with solid targets

Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations. The spatial strength distribution of magnetic fields can be accurately predicted by calculating the net flow caused by the superposition of source flow and return flow of hot electrons. The theoretical model established shows good agreement with the simulation results, indicating that the magnetic-field strength scales positively to the temperature of hot electrons. This provides us a way to improve the magnetic-field generation by using a micro-structured plasma grating in front of the solid target. Compared with that for a common flat target, hot electrons can be effectively heated with the well-designed grating size, leading to a stronger magnetic field. The spatial distribution of magnetic fields can be modulated by optimizing the grating period and height as well as the incident angle of the laser pulse.

A compact 51.6-W, 26-[formula omitted]J, Yb-doped all-fiber integrated CPA system through quasi-rectangular pulse pre-shaping

A compact 51.6-W, 26-μJ all-fiber integrated Yb-doped femtosecond laser source with pulse durations of 692 fs despite ∼18π nonlinear phase shift accumulation in the main amplifier is demonstrated by using fiber quasi-rectangular pulse pre-shaping. The numerical results are in good agreement with the experiment. Due to the advantages of an all-fiber spliced structure and a minimal pulse stretching ratio (from 26.3 ps to ∼70 ps), just a small size of gratings and a short separation distance between the two gratings in the compressor is required. Therefore, the laser source is exceedingly compact, robust, cost-effective, and easy to assemble. This technique is anticipated to accelerate the use of fiber femtosecond lasers in industrial applications.

Oral acuity, particle size sensitivity, and food texture preferences in an older adult population

Changes in sensory sensitivity occur as we age but changes in food texture sensitivity in the older adult population remain poorly understood. The objective of this study was to describe the relationship between oral tactile acuity, mouth behaviour, and particle size sensitivity and their potential influence on preferred food textures in older adults. Older adults (n = 79; mean age = 69.7 yrs) participated in an evaluation of oral health and texture perception through survey measurements of mouth behaviour, and preferred food textures. Oral tactile acuity was assessed using the Grating Orientation Task (GOT) with three grating sizes (0.5, 0.75, and 1.5 mm). Food particle sensitivity was evaluated through a difference-from-control (DFC) sensory assessment of ground quinoa mixed into yogurt, utilizing three particle size ranges (<75, 150–250, and 500–600 μm). The results revealed that the sample containing 500–600 mm particle sizes yielded a higher difference (DFC) score compared to the samples with < 75 μm and 150–250 μm particles (p < 0.05). However, no significant relationship (p > 0.05) was found between the R-indices obtained from the GOT assessments and DFC scores, indicating no association between oral tactile acuity and particle size sensitivity. Liking ofcreamy, leafy, slippery, sticky, with skins,andcombinationfood textures was significantly positively associated with the 0.5 mm GOT tool R-index values, suggesting higher oral acuity influences liking of specific food textures. Significant differences (p < 0.05) were present in liking of food textures among different mouth behaviour groups. These results suggest that texture perception and sensitivity influence texture acceptance in older adults.

Concept for a critical-angle transmission grating spectrometer for the AXIS probe

The Advanced X-ray Imaging Satellite (AXIS) is a probe-class mission concept with a large collecting area with a point-spread-function of order 1 to 2 arcsec. We describe a possible X-ray grating spectrometer (XGS) that could be added to AXIS with minimal design changes to the telescope itself and costs a small fraction of the total mission budget. The XGS would be based on critical-angle transmission (CAT) gratings, a technology already matured for Arcus and Lynx. Using detailed ray-tracing, we investigate several options for subaperturing that provide a trade-off between effective area and spectral resolving power. Depending on how much of the full aperture is covered with gratings (e.g., 17% to 100%), we find a high spectral resolving power up to λ / Δλ = 4000 can be achieved with effective area of 1500 cm2 in the 1.2 to 2.8 nm range or λ / Δλ = 6000 with effective area 500 cm2. An important benefit of CAT gratings is that they are mostly transparent at high energies, and thus hard x-rays can still be used for simultaneous imaging spectroscopy. We study different grating sizes and other enhancements, but even in the basic configuration an XGS can be added to AXIS to provide high-resolution spectral capabilities, opening a range of new science investigations. Our ray-tracing shows that this concept is mature and can be added to AXIS with minimal impact on other instruments. We discuss one exemplary science case that would be enabled by the XGS.

The tradeoffs between grating lobes and larger array pitch using null subtraction imaging

Null Subtraction Imaging (NSI) is a new beamforming technique for producing B-mode images that results in high spatial resolution and low computational cost compared to other high-spatial resolution imaging techniques. Previous work has demonstrated that in addition to a narrow main lobe and low side lobes, NSI can also reduce or mitigate grating lobes. Grating lobes can appear when the wavelength of ultrasound is larger than the pitch of the array and these grating lobes can result in imaging artifacts. Lower grating lobes on a larger pitch array could allow larger linear arrays for abdominal imaging with lower element count. Experiments were conducted to quantify the tradeoff between grating lobe levels and pitch size when using NSI. NSI was able to reduce grating lobes by up to 19dB with an element pitch of five times the wavelength. The effects of the DC offset (a tunable parameter of NSI) on grating lobe reduction were also testedand found that NSI with a lower DC offset provides greater reduction in grating lobes, with up to 40dB reduction. The level of grating lobe reduction versus the depth of a target was also testedand found a slight decrease in grating lobe reduction at greater depths.

Different gain modulations of selective attention at short and long cue-target delays.

Previous studies have tested attentional gain patterns, for example, within the normalization model of attention (NMoA), by altering the relative sizes of the attention field and stimuli. Existing studies have not investigated whether the gain patterns of altering the relative exogenous cue size as compared with the target stimuli matches the prediction of NMoA and whether these gain patterns exist in the late stage of attentional processing. To resolve these questions, the present study maintained the target grating size and changed the exogenous cue size in both short and long cue-target onset asynchronies (CTOAs) conditions. The results revealed response gain for small cue/large target size conditions and contrast gain for large cue/small target size conditions, which was consistent with the NMoA. However, we observed the decrease in the contrast gain factor only with long CTOAs, regardless of whether the cue size was relatively small or large. This indicated that NMoA-related effects based on the relative attentional field dominated in the early stage and that the contrast gain dominated in the late stage.

Effect of Changing the Shape and Size of Inlet Area of Grates on the Hydraulic Efficiency of Urban Rainstorm Drainage Systems

Urban rainstorm drainage systems are used to collect the surface runoff from streets and other land surfaces through grate or curb openings that convey it to the drains. The quantity of surface runoff that is not discharged to the urban rainstorm drainage systems due to inadequate grate size or because the grate capacity is exceeded can cause flooding, immoderate hazards to drivers and pedestrians, and disrupt urban activities. This study aims to carry out experimental work to investigate the hydraulic efficiency of urban rainstorm drainage systems using different types of grates (shape and size of inlet area) for harvesting excess rainwater. Different grate shapes (five) with different inlet areas were investigated, as well as using three relative grate inlet areas (26%, 51%, and 64%). The results of the experimental work indicated that the best grate shape is the grate type 4 which provided the smallest reduction in discharge efficiency within 8.7%. The results specified that changing the size of the inlet area of grates from (26%) to (64%) has a significant impact on urban rainstorm drainage systems efficiency which decreased by 4%. In addition, the dimensional analysis principle with multi regression analysis were used to develop an empirical equation to compute the efficiency of urban rainstorm drainage systems. The relation between grate shapes and the relative inlet area with the efficiency of grate capture provides an indication to the decisionmakers to increase the time period for maintenance which will save the cost for further maintenance. The presented empirical equation can help decisionmakers for monitoring the current situation of grate blockage (relative grate inlet areas) and the corresponding efficiency. This study is beneficial for future road drainage system construction to avoid problems by assessing the performances of the current drainage systems and proposing mitigation measures to avoid improper functioning. Finally, this methodology can help to improve the efficiency of urban rainstorm drainage systems that can reduce the risks of urban floods.

Optimizing two-dimensional polarization-diversity metagrating couplers for silicon photonics

Polarization-diversity couplers are promising industrially scalable optical devices that can couple optical signals with unknown polarization states into silicon photonic chips. Here we propose a novel, to the best of our knowledge, two-dimensional (2D) metagrating coupler (MGC) for the polarization-diversity system, which improves its coupling efficiency for both polarizations. Compared with the previously reported 2D grating couplers (GCs) with identical grating cells, the proposed apodized design gradually changes the aspect ratio and orientation angles of the elliptical patterns simultaneously. This 2D array of the varied grating cells modulates the diffracted mode field patterns and phases locally, and achieves a better overlap with the Gaussian fiber modes for both polarizations. The peak coupling loss (PCL) for the S-polarized and P-polarized light are − 1.6 d B and − 2.7 d B , respectively. The calculated polarization dependent loss is lower than 0.2 dB from 1522 nm to 1540 nm. The device is robust to the fabrication tolerance and fiber misalignment. The simulated fabrication tolerance analysis show that the etch depth error of ±20 nm results in less than 0.3 dB and 0.1 dB PCL drop, while the grating cell feature size error of ± 40 n m results in less than 0.6 dB and 0.2 dB PCL drop for both types of polarization light, respectively. The fiber misalignment should be within the range from − 2 µ m to + 2 µ m in two perpendicular directions, and the coupling angle deviation should be within the range from − 3 ∘ to + 3 ∘ , in order to assure 0.5 dB penalty loss for both polarizations. The performance of the design is insensitive to the mask misalignments. To assure 0.5 dB penalty loss for both polarizations, Δ θ is suggested to be within the range from − 3 ∘ to + 3 ∘ .

Optical methods for measuring the feature size of optical diffraction gratings with nano-meter accuracy and implementation of suitable feedback control loops

Surface relief diffraction gratings offer a high flexibility in their design and thus allow to synchronize their optical performance with the specific requirements of the underlying application. However, the accuracy and the specific control of the manufacturing processes are of vital importance. In this contribution, we present optical methods relying on white-light ellipsometry and how they can be exploited for the measurement of the critical dimensions of manufactured surface relief grating structures. We will furthermore present suitable processes (relying on atomic layer deposition) and how they are used in a feedback loop to control the grating’s feature sizes on the nanometer scale.

Assessment of Spatial Lingual Tactile Sensitivity using a Gratings Orientation Test.

Individual thresholds by R-index estimates are calculated using a gratings orientation test (6 different tools of increasing grating size from 0.20-1.25 mm) to assess spatial lingual tactile sensitivity. During the experiment, the subjects are blindfolded and asked to specify the orientation of the grating (either horizontal or vertical) placed on the tongue. R-index is based on Signal Detection Theory (SDT), and it is an estimated probability of correctly identifying a target stimulus (the signal, e.g., the correct orientation) compared to an alternative stimulus (the noise, e.g., the incorrect orientation). Once the R-index values for each subject and each tool dimension are calculated, it is possible to derive the individual threshold by interpolating the two R-indices immediately below and above the established cut-off (typically 75%) based on one-sided R-index critical values. This procedure can be helpful in the medical field to study the association between oral tactile sensitivity, speech clarity, and swallowing disorders, as well as in sensory and consumer studies to explore individual variation in texture perception, food preferences, and eating behavior.

Design of Fiber-Tip Refractive Index Sensor Based on Resonant Waveguide Grating with Enhanced Peak Intensity

Resonant waveguide gratings (RWG) are widely used as on-chip refractometers due to their relatively high sensitivity to ambient refractive index changes, their possibility of parallel high-throughput detection and their easy fabrication. In the last two decades, efforts have been made to integrate RWG sensors onto fiber facets, although practical application is still hindered by the limited resonant peak intensity caused by the low coupling efficiency between the reflected beam and the fiber mode. In this work, we propose a new compact RWG fiber-optic sensor with an additional Fabry-Pérot cavity, which is directly integrated onto the tip of a single-mode fiber. By introducing such a resonant structure, a strongly enhanced peak reflectance and improved figure of merit are achieved, while, at the same time, the grating size can be greatly reduced, thus allowing for spatial multiplexing of many sensors on a tip of a single multi-core fiber. This paves the way for the development of probe-like reflective fiber-tip RWG sensors, which are of great interest for multi-channel biochemical sensing and for real-time medical diagnostics.

Multistep pulse compressor for 10s to 100s PW lasers.

High-energy tens (10s) to hundreds (100s) petawatt (PW) lasers are key tools for exploring frontier fundamental researches such as strong-field quantum electrodynamics (QED), and the generation of positron-electron pair from vacuum. Recently, pulse compressor became the main obstacle on achieving higher peak power due to the limitation of damage threshold and size of diffraction gratings. Here, we propose a feasible multistep pulse compressor (MPC) to increase the maximum bearable input and output pulse energies through modifying their spatiotemporal properties. Typically, the new MPC including a prism pair for pre-compression, a four-grating compressor (FGC) for main compression, and a spatiotemporal focusing based self-compressor for post-compression. The prism pair can induce spatial dispersion to smooth and enlarge the laser beam, which increase the maximum input and output pulse energies. As a result, as high as 100 PW laser with single beam or more than 150 PW through combining two beams can be obtained by using MPC and current available optics. This new optical design will simplify the compressor, improve the stability, and save expensive gratings/optics simultaneously. Theoretically, the output pulse energy can be increased by about 4 times using the MPC method in comparison to a typical FGC. Together with the multi-beam tiled-aperture combining method, the proposed tiled-grating based tiled-aperture method, larger gratings, or negative chirp pulse based self-compression method, several 100s PW laser beam is expected to be obtained by using this MPC method in the future, which will further extend the ultra-intense laser physics research fields.

Pupil size is modulated by the size of equal-luminance gratings.

Pupil size changes with light. For this reason, researchers studying the effect of attention, contextual processing, and arousal on the pupillary response have matched the mean luminance of their stimuli across conditions to eliminate the contribution of differences in light levels. Here, we argue that the match of mean luminance is not enough. In Experiment 1, we presented a circular sinewave grating on a gray background for 2 seconds. The area of the grating could be 3°, 6°, or 9°. The mean luminance of each grating was equal to the luminance of the gray background, such that regardless of the size of the grating there was no change in mean luminance between conditions. Participants were asked to fixate the center of the grating and passively view it. We found that in all size conditions, there was a pupil constriction starting at about 300 ms after stimulus onset, and the pupil constriction increased with the size of the grating. In Experiment 2, when a small grating was presented immediately after the presentation of a large grating (or vice versa), the pupil constriction changed accordingly. In Experiment 3, we replicated Experiment 1 but had the subjects perform an attention-demanding fixation task in one session, and passively view the stimuli in the other. We found that the main effect of task was not significant. In sum, our results show that stimulus size can modulate pupil size robustly and steadily even when the luminance is matched across the different stimuli.

Cost-Efficient Printing of Graphene Nanostructures on Smart Contact Lenses.

Smart contact lenses have been put forward for years, but there is still no commercial product in the market; the high cost due to expensive fabrication techniques could be one of the reasons. In this paper, first, a cost-efficient and reliable route to fabricate graphene grating on contact lens was designed and demonstrated based on the direct laser interference patterning graphene film on commercial contact lenses using an Nd:YAG laser. The thickness of the film and the interference angle have been taken into consideration. Optical characterization and simulation have been applied to evaluate the quality of our final achieved grating patterns with a grating size from 0.92 to 3.04 μm. Two-dimensional (2D) patterns could also be obtained through double-time laser interference. Contact angles for samples with different interference angles were presented considering the service environment of smart contact lenses. Of course, the conductivity of the samples was evaluated using a four-probe method. The most conductive sample had the sheet resistance lower than 30 Ω/sq. This research study highlighted the possibility of patterning graphene with the laser ablation method and provided a candidate solution for the fabrication of smart contact lenses under controlled cost.

Configuration Model of a Grating Pair Pulse Compressor

This paper proposes the unifying model that describes configuration of a wide-aperture laser compressor formed by pairs of parallel diffraction gratings. The model couples eight independent parameters of broadband laser radiation, diffraction gratings, and pulse compressor configuration. A new analytical method to describe delays in a wide-aperture beam propagating through a system of several grating pairs is proposed based on separate analysis of monochromatic and wavelength-dependent delays. Model-based optimization can be applied to spectral, phase, temporal, spatial, and energy characteristics of radiation at the output of a high-power laser facility. It is shown that the model allows minimizing the required size of diffraction gratings and increasing the cross section of the light beam at the output of a Nd-glass laser facility. A new multi-paired architecture of the compressor is described.

Talbot-Lau x-ray phase-contrast setup for fast scanning of large samples

Compared to conventional attenuation x-ray radiographic imaging, the x-ray Talbot-Lau technique provides further information about the scattering and the refractive properties of the object in the beam path. Hence, this additional information should improve the diagnostic process concerning medical applications and non-destructive testing. Nevertheless, until now, due to grating fabrication process, Talbot-Lau imaging suffers from small grating sizes (70 mm diameter). This leads to long acquisition times for imaging large objects. Stitching the gratings is one solution. Another one consists of scanning Talbot-Lau setups. In this publication, we present a compact and very fast scanning setup which enables imaging of large samples. With this setup a maximal scanning velocity of 71.7 mm/s is possible. A resolution of 4.1 lines/mm can be achieved. No complex alignment procedures are necessary while the field of view comprises 17.5 × 150 cm2. An improved reconstruction algorithm concerning the scanning approach, which increases robustness with respect to mechanical instabilities, has been developed and is presented. The resolution of the setup in dependence of the scanning velocity is evaluated. The setup imaging qualities are demonstrated using a human knee ex-vivo as an example for a high absorbing human sample.

High incidence of rainbow glare after femtosecond laser assisted-LASIK using the upgraded FS200 femtosecond laser

BackgroundTo compare the incidence of rainbow glare (RG) after femtosecond laser assisted-LASIK (FS-LASIK) using the upgraded FS200 femtosecond laser with different flap cut parameter settings.MethodsA consecutive series of 129 patients (255 eyes) who underwent FS-LASIK for correcting myopia and/or astigmatism using upgraded WaveLight FS200 femtosecond laser with the original settings was included in group A. Another consecutive series of 129 patients (255 eyes) who underwent FS-LASIK using upgraded WaveLight FS200 femtosecond laser with flap cut parameter settings changed (decreased pulse energy, spot and line separation) was included in group B. The incidence and fading time of RG, confocal microscopic image and postoperative clinical results were compared between the two groups.ResultsThere were no differences between the two groups in age, baseline refraction, excimer laser ablation depth, postoperative uncorrected visual acuity and refraction. The incidence rate of RG in group A (35/255, 13.73%) was significantly higher than that in group B (4/255, 1.57%) (P < 0.05). The median fading time was 3 months in group A and 1 month in group B (P > 0.05).The confocal microscopic images showed wider laser spot spacing in group A than group B. The incidence of RG was significantly correlated with age and grouping (P < 0.05).ConclusionsThe upgraded FS200 femtosecond laser with original flap cut parameter settings could increase the incidence of RG. The narrower grating size and lower pulse energy could ameliorate this side effect.

Edge spread function of Talbot phenomenon

The paper presents and analyses the edge spread function of Talbot phenomenon—self-imaging of a periodical structure in given distances behind a template, if the template is illuminated by a plane wave. This phenomenon has many applications in optical metrology and in industry. Detailed mathematical analysis with an amplitude grating illuminated by a monochromatic plane wave is performed, and a simple relation for the calculation of the edge spread function width of Talbot imaging of Ronchi grating is shown which allows a simple analysis of the edge spread function for different grating sizes without any difficult calculations. The results bring a complete insight to the problematics and it can serve as a great theoretical background in many applications which utilize Talbot phenomenon.

Preparation of hydrophobic surface on titanium by micro-rolling and laser diffusion carbonitriding

The application of rolling for fabricating grate on titanium stripe has been explored in this paper. Then the mechanically robust Ti(C,N) diffusion layer was synthetized directly on the grates by laser carbonitriding in the mixture gas of nitrogen and methane. The results shows that the carbonitriding process is accelerated by temperature enhancement with decreasing scanning speed. The Ti(C,N) diffusion layer is kept at 2 μm in thickness, when the scanning speed is smaller than 4 mm/s. The contact angle increases from 20° to 143.6° by designing an appropriate grate size and surface roughness. Meanwhile, the relationship between hydrophobicity, hardness performance and scanning speed is also discussed. The hardness of diffusion layer increases with decreasing laser scanning speed, and is up to 11.2 GPa. The surface structure and hydrophobic state are maintained after three cycles of sandpaper abrasion, which has improved the robustness of surface grate.

Properties of pattern and component direction-selective cells in area MT of the macaque.

Neurons in area MT/V5 of the macaque visual cortex encode visual motion. Some cells are selective for the motion of oriented features (component direction-selective, CDS); others respond to the true direction of complex patterns (pattern-direction selective, PDS). There is a continuum of selectivity in MT, with CDS cells at one extreme and PDS cells at the other; we compute a pattern index that captures this variation. It is unknown how a neuron's pattern index is related to its other tuning characteristics. We therefore analyzed the responses of 792 MT cells recorded in the course of other experiments from opiate-anesthetized macaque monkeys, as a function of the direction, spatial frequency, drift rate, size, and contrast of sinusoidal gratings and of the direction and speed of random-dot textures. We also compared MT responses to those of 718 V1 cells. As expected, MT cells with higher pattern index tended to have stronger direction selectivity and broader direction tuning to gratings, and they responded better to plaids than to gratings. Strongly PDS cells also tended to have smaller receptive fields and stronger surround suppression. Interestingly, they also responded preferentially to higher drift rates and higher speeds of moving dots. The spatial frequency preferences of PDS cells depended strongly on their preferred temporal frequencies, whereas these preferences were independent in component-selective cells. Pattern direction selectivity is statistically associated with many response properties of MT cells but not strongly associated with any particular property. Pattern-selective signals are thus available in association with most other signals exported by MT.