Spot Size Measurements Research Articles

SPOT SIZE COMPARISONS ON OIL– AND WATER–SENSITIVE PAPER

Water and oilsensitive paper (WSP and OSP) was attached to tree leaves and to a tower bracket between trees.Petroleum spray oil was applied at a constant rate in four concentrations of spray oil in water (1:5.9, 1:10, 1:50, and 1:100)with 17 treatments. WSP and OSP were sprayed in a laboratory with 8001 and 8004 flat fan nozzles. Spot size on oil andwatersensitive paper, placed at the same location for the same spray condition, were compared by assuming the spots camefrom the same droplet size population. The spot sizes were sorted by size and divided into 25 classes with the same numberof spots in each class. The mean size of each population was calculated for each size class and the ratio of water to oil spotswas calculated. To reduce the effect of spot overlap, only sprayed samples with low populations (less than 20% coverage)of water and oil spots were used. Measured spot size ratios were compared to ratios calculated from droplet diameter ratioscomputed from volume mixtures and from known spread factors on water and oil sensitive paper. Water:oil spot size ratiospredicted using known mixture ratios and spread factors agreed quite well with laboratory measured spot size ratios. However,spot size ratios measured for field experiments did not agree with predicted values. This may have been due to larger waterspots touching, or oil spots separating into several globules as the water portion of the spray droplet evaporates.

Temperature and energy spread investigations of alloy LMIS

Emitters wetted with Ga, Au 73Ge 27, Au 77Ge 14Si 9 and Co 36Nd 64 alloys were investigated with regard to the influence of the source temperature on the current-voltage characteristics and the energy spread of the different emitted ion species. The latter was measured using a system that includes an ExB mass filter and a retarding field energy analyser. The energy spread significantly affects the available spot size in focused ion beam (FIB) systems and depends also on the emission current, the charge state, and the mass of the ions or clusters. The influence of the source parameters, temperature and energy spread, on the beam performance in terms of spot size measurements is demonstrated with a 70 keV Ge 2+ beam using the FIB system IMSA - 100.

Laser photocoagulation spot-size errors stemming from the refractive state of the surgeon’s eye

PurposeMeaningful errors in photocoagulation spot size may result from several factors. In this article we discuss one major factor, namely, fluctuations in the surgeon’s accommodative state, coupled with an inaccurate setting of the slit-lamp oculars. DesignExperimental study. MethodsWe analyzed and tested the optics of slit-lamp mounted lasers. Varying the ocular setting is correlated with measurements of the actual spot size obtained with each system. Main outcome measureThe spot size obtained. ResultsThree distinct, but related, phenomena that may lead to spot size errors are defined: (1) focusing the laser spot as opposed to focusing the retinal image; (2) instrument misalignment; (3) inadvertent accommodation. ConclusionThe ocular setting must be meticulously calibrated to produce a true spot-sized burn. At the 50 μm setting, each diopter of induced accommodation, or erroneous ocular setting, almost doubles the actual spot size obtained. With large (500 μm) spot size settings, the defocused delivery system is more prone to spot-size errors in contrast with parfocal lasers.

Résolution spatiale de la caméra thermique à source volante

The photothermal camera (flying spot camera) is an instrument fer non destructive testing, where a heat source and an infrared (IR) detector together scan the material surface. The detector monitors the temperature rise induced by the moving heating spot. This technique has been used for many years for thin coatings characterisation and for crack detection. We did not find any quantitative analysis about its spatial resolution in the literature. Our objective was thus to perform a theoretical analysis on the flying spot camera resolution. It actually depends on the photothermal ‘accident’ that is met during the scanning. Due to their importance and/or occurrence in NDT, the following photothermal ‘perturbations’ were analysed: emissivity variation, absorptivity variation, joint emissivity and absorptivity variations, and finally a thermal resistance perpendicular to the surface (model for open cracks). For all cases, we discussed the influence of various experimental parameters: heating spot size, IR measurement spot size, scanning velocity…

Influence of optical aberrations on laser-induced plasma formation in water and their consequences for intraocular photodisruption

The influence of spherical aberrations on laser-induced plasma formation in water by 6-ns Nd:YAG laser pulses was investigated for focusing angles that are used in intraocular microsurgery. Waveform distortions of 5.5lambda and 18.5lambda between the optical axis and the 1/e(2) irradiance values of the laser beam were introduced by replacement of laser achromats in the delivery system by planoconvex lenses. Aberrations of 18.5lambda increased the energy threshold for plasma formation by a factor of 8.5 compared with the optimized system. The actual irradiance threshold for optical breakdown was determined from the threshold energy in the optimized system and the spot size measured with a knife-edge technique. For aberrations of 18.5lambda the irradiance threshold was 48 times larger than the actual threshold when it was calculated by use of the diffraction-limited spot size but was 35 times smaller when it was calculated by use of the measured spot size. The latter discrepancy is probably due to hot spots in the focal region of the aberrated laser beam. Hence the determination of the optical-breakdown threshold in the presence of aberrations leads to highly erroneous results. In the presence of aberrations the plasmas are as much as 3 times longer and the transmitted energy is 17-20 times higher than without aberrations. Aberrations can thus strongly compromise the precision and the safety of intraocular microsurgery. They can further account for a major part of the differences in the breakdown-threshold and the plasma-transmission values reported in previous investigations.

Laser Weld Penetration Estimation Using Temperature Measurements

Penetration depth is an important factor critical to the quality of a laser weld. This paper presents a 3D heat conduction model with a moving line source to correlate the temperature measured on the bottom surface of the workpiece to the weld penetration, weld bead width and welding speed. Temperatures on the bottom surface of the workpiece are measured using infrared thermocouples located behind the laser beam. The averaging effect due to the temperature measurement spot size is analyzed. This paper provides a model-based approach for laser weld penetration monitoring instead of a pure empirical correlation between a measured signal (e.g., acoustic, infrared) and the penetration depth. Experiments were conducted to compare the depth estimation based on the model to bead-on-plate welds on low carbon steel plates of varying thickness at different laser power levels and speeds. It is shown that the temperature on the bottom surface is a consistent indicator of penetration depth and that the correlation is also sensitive to the sensor location as well as other process conditions such as weld shape, width, and the plate thickness. The proposed model is computationally efficient and is suitable for on-line process monitoring application.

Experiments of high energy gain laser wakefield acceleration

The wakefield acceleration of electrons has a great potential for the future accelerator because of its high accelerating field gradient. We have obtained over 100 MeV acceleration gain by the wakefield generated by a 2 TW Ti : sapphire laser system. In the acceleration experiment, the 17 MeV electrons from a linac were used for the injection beam. The synchronization between the RF signal and the laser pulse was achieved within the time jitter of 3.7 ps. Due to the self-focusing and ionization, a long propagation length and high field gradient were realized. The self-focusing effect of the laser was confirmed by the laser spotsize measurement along the beam axis. The plasma density oscillation was measured by using the frequency domain interferometry. The acceleration gain expected from the plasma density measurement was consistent with the result of the acceleration experiments.

Accuracy Depending on Scanning Angle in Dynamic Spot Size Measurement Method for an Optical Disk Drive

The spot size has been measured by chopping the beam spot with a knife edge on an optical disk. Tangential and radial spot sizes are measured with different two angled knife edges: θ1-edge and θ2-edge. In this paper, the errors in the measurement of spot sizes caused by the error in the scanning angle and the scanning velocity are described. The result of the theoretical analysis gives the best combinations of the scanning angles which are θ1=0°, θ2=±45° with the radial direction. For example, if the angle error of θ1 and θ2 obtained experimentally 0.64°, then the calculated error of the radial spot size is 2.2%. The analyzed error shows a good agreement with the experimental results. It was analytically observed that the influence of the scanning velocity error on the error of the measured spot sizes can be practically ignored using this method.

Nuclear microprobe analysis and imaging: Current state of the art performances

The current state-of-the-art performances claimed for nuclear microbeam spatial resolutions are: (a) 400 nm spot sizes for high current (100 pA) proton beams, (b) 400 nm for high current alpha particle beams, (c) 100 nm for low proton current (<0.1 pA) applications such as Scanning Transmission Ion Microscopy (STIM) and Ion Beam Induced Charge (IBIC) and (d) 50 nm for low current alpha particles. These claims, however, have been undermined not only by the lack of a common and generally accepted resolution standard, but also by the lack of a consistent approach between groups regarding a recognised method of beam spot measurement. The lack of a definitive method for assessing spatial resolution is hindering the future development of nuclear microprobes to higher spatial resolutions. We require the manufacture of resolution standards specifically tailored for nuclear microprobe spot size measurements, for both high and low current operations. Until such resolution standards are available, one commercially available standard which has high potential for high current proton beam resolution tests is the Ebeam test chip manufactured for the characterisation of electron beam testers. This chip has patterns as small as 0.5 μm in size produced in 0.5 μm thick aluminium by direct electron beam writing. Using both analytical Particle Induced X-ray Emission (PIXE) imaging and PIXE line scans, the nuclear microscope facility at the National University of Singapore has demonstrated spatial resolutions of less than 400 nm for a 100 pA beam of 2 MeV protons. Low current resolution standards have more stringent requirements. One potential standard tested in Singapore is a prototype self-supporting X-ray mask used in X-ray lithography. This test standard, however, is not commercially available at the moment, is fragile and therefore difficult to handle and easily fractured. Using off-axis STIM imaging and line scanning over this mask, the NUS nuclear microscope facility has demonstrated beam spot sizes less than 130 nm for a 1 pA 2 MeV proton beam.

Ultrasonic wavefront distortion caused by human abdominal wall layers

The relative importance of the fat and muscle layers of the human abdominal wall in producing ultrasonic wavefront distortion has been assessed based on direct measurements. Specimens employed included 6 whole abdominal wall specimens and 12 partial specimens obtained by dividing each whole specimen into a fat and a muscle layer. In the measurements, a hemispheric transducer transmitted a 3.75-MHz ultrasonic pulse through a tissue section maintained at 37°. The received wavefront was measured by a linear array translated in the elevation direction to form a two-dimensional aperture with overall dimensions 92.16×46.08 mm2 and a measurement spot size of 0.72×1.44 mm2. Differences in arrival time and energy level between the measured waveforms and computed references that account for geometric delay and spreading were calculated. After correction for the effrects of geometry, the received waveforms were synthetically focused at 180 mm. The characteristics of the distortion produced by each specimen and the quality of the resulting foci were analyzed and compared. The results indicate that both fat and muscle layers contribute significantly to the distortion of ultrasonic beams by the abdominal wall. However, the spatial characteristics of the distortion produced by fat and muscle layers differ substantially, and the total distortion produced by the abdominal wall is not equivalent to the sum of the distortion produced by the layers.

A 1060 nm diode laser system for dynamically probing silicon detectors

Abstract We have constructed a 1060 nm laser system which has been used to dynamically probe silicon microstrip detectors. A diode laser is coupled to a single mode fiber with a less than 10 μm measured spot size. The laser is driven by a nanosecond pulse with sub-nanosecond rise and fall times. The fast response and small spot size allow for measurements of such quantities as time walk in microstrip detectors. The system has been used to generate 5–100 fC of charge in a 300 μm thick silicon microstrip detector. The laser also has been used in localized depletion voltage measurements and to test the integrity of sensors wire bonded to readout electronics.

Effects of focal spot size on caries diagnosis with D and E speed images

Annual measurement of the x-ray unit focal spot size has been recommended by the American Academy of Oral and Maxillofacial radiology as part of the dental radiographic quality control program. This study compares the effects of focal spot size on caries diagnosis. Three x-ray units with small, medium, and large focal spot sizes were used to produce bite-wing images on extracted teeth mounted in acrylic bases. Randomized films were scored for lesion presence and depth by two general dentists. Weighted kappa statistics were used to evaluate the agreement of reviewer caries diagnosis by film speed and focal spot size. Comparisons of caries cells with small versus medium and small versus large focal spot size produced weighted kappa statistics = 0.72 and 0.70, respectively. Differences in caries calls were greater because of film speed rather than focal spot size. The results of this study suggest that the clinical significance of varied focal spot size is negligible. The value of annual measurement of focal spot size is questionable, and its recommendation should be revisited.

Original method for measurement of optical mode fields

We report on a new method for measurement of mode spot sizes of fibers or waveguides (Ti-diffused or proton-exchanged waveguides on LiNbO(3)) that uses neither camera nor optics and works at any wavelength with a 1-μm resolution. The measurements are in good agreement with a finite element simulation.

Measurements of ultrasonic pulse distortion produced by the chest wall

Ultrasonic wavefront distortion produced by transmission through human chest wall specimens was measured. Pulses with a center frequency of 2.3 MHz were received over a 20.00×20.16 mm2 area with a measurement spot size of 0.21×0.40 mm2 after propagation through a chest wall specimen. Secondary wavefronts produced by interactions between transmitted pulses and structures of the rib cage sometimes disrupted the main wavefront and interfered with the determination of wavefront distortion caused by soft tissue inhomogeneities. Differences in arrival time and energy level between 11.60×14.28 mm2 regions of the measured waveforms that did not include secondary wavefronts and references that account for geometric delay and spreading were computed. For 16 different intercostal spaces, the average rms value of the arrival time fluctuations was 21.3 ns with a mean correlation length of 2.50 mm. The energy level fluctuations had an average rms value of 1.57 dB and a correlation length of 1.98 mm. The results indicate that soft tissue inhomogeneities in chest wall specimens significantly distort ultrasonic pulses in the low MHz frequency range, although the magnitude of this distortion is noticeably smaller than that measured for abdominal wall specimens at 3.75 MHz [Hinkelman etal., J. Acoust. Soc. Am. 95, 530–541 (1994)].

Ray matrix for Gaussian beam propagation in a nonlinear medium: experimental results

The validity of a ray-matrix formulation of Gaussian beam propagation in a liquid nonlinear medium exhibiting self-defocusing is examined experimentally. By comparing the measured spot size of a Gaussian laser beam passing through the medium with the calculated spot size, it was found that the theory is consistent with the experimental results as long as the waist position of the input beam is not close to the exit surface of the medium.

Book reviews

This booklet in the IPSM Report Series describes techniques for the physical assessment of dental radiology equipment — both simple intraoral and panoramic X-ray equipment. The first chapter describes methods and gives expected results for measurement of tube output, exposure time, kilovoltage, filtration and focal spot size.

Measurement of focal spot size in mammography X-ray tubes.

Three different measurement techniques for estimating the size of focal spots in X-ray tubes are described. These are the pin-hole, the slit and the star pattern or resolution pattern, and all are well known. Results are reported for a number of modern mammography X-ray tubes employed in a screening programme, using all three techniques. The results are compared with each other and with makers' specifications, IEC tolerances and UK Department of Health guidelines. Agreement between slit and star pattern results is generally within a few per cent, while pin-hole results are usually appreciably smaller. Although the slit technique is the most reliable for estimating focal spot size, both the others have a useful role, especially in revealing focal spot condition. Compliance with makers' specifications is usually demonstrated, but compliance with Department of Health guidelines is only found on the width of broad foci.

1. Measurement of Focal Spot Size of Heavy Loaded X Ray Tubes

In order to assure safety of both patient and operator, and to provide uniform quality radiographs, it is necessary to perform periodic calibration of diagnostic X-ray equipment. A basic parameter of diagnostic equipments and its image sharpness is the size (and shape the energy distribution) of the focal spot as viewed along the central X-ray beam. This size determines the resolution possible with the equipment and also determines the heat characteristics of an anode. A fine focus tube gives high resolution but causes high local heating of target. In past, the pin-hole and star pattern image measurement for evaluation of resolution have been widely used, but it produced blurring and inaccuracy of image. So newly inverted Ug-meter has advantage in more convenient measurement method and less out-put bias than other image measurement. The authors intended to compare measured focal size between Ug-meter and focal spot test tool, changed state from setting to now of units.

Periodic exponential ruling for the measurement of Gaussian laser beam diameters

The spot size measurement of a Gaussian laser beam is extended to wide dynamic range through the formulation of a novel exponential grating. It is found that the exponential grating provides accurate measurement for both extremely small and large Gaussian beam diameters and proves to be superior to Ronchi, triangular, and sinusoidal rulings.

Testing mammography equipment: evolution over a 4-year period.

The results of quality control (QC) tests on 70 mammography units in Southern California from 1986 to 1990 are reported. Thirteen facilities, selected because they housed all of the mammography units in three communities involved in a National Institutes of Health research project, had their units tested twice at an interval of 1 year. Fourteen self-selected units were also tested twice at intervals ranging from 1-3 years. Forty-three self-selected units in 31 additional facilities had testing only once. All 70 units underwent measurement of focal spot size or resolution, tube output, half-value layer (HVL), automatic exposure control (AEC) accuracy, relative kVp accuracy, mean glandular dose, and imaging of several test objects. The test results for the units tested once showed no significant differences compared to those tested twice. For the latter, once the units were tested and determined to be acceptable, retesting showed differences only in overall film optical density, dose, and AEC performance.