Design, simulation, and experimental validation ofa segmented beam-shaping integrator mirror.

The purpose of this study is to (i) investigate the impact of various air gaps in conjunction with a range shifterof 7.5cm water-equivalent-thickness(WET) on in-air spot size of a pencil proton beam at the isocenter and off-axis points, and (ii) comparethe treatment planning system (TPS) calculated spot sizes against the measured spot sizes. A scintillation detector has been utilized to measure the in-air spot sizes at the isocenter. The air gap was varied from 0 to 35cm at an increment of 5cm. For each air gap, a single spot pencil proton beam of various energies (110-225 MeV) was delivered to the scintillation detector. By mimicking the experimental setup in RayStation TPS, proton dose calculations were performed using pencil beam (RS-PB) and Monte Carlo (RS-MC) dose calculation algorithms. The calculated spot sizes (RS-PB and RS-MC) were then compared against the measured spot sizes. For a comparative purpose, the spot sizes of each measured energy for different air gaps of (5-35cm) were compared against that of 0cm air gap. The results of the 5cm air gap showed an increase in spot size by ≤ 0.6mm for all energies. For the largest air gap (35cm) in the current study, the spot size increased by 3.0mm for the highest energy (225MeV) and by 9.2mm for the lowest energy (110MeV). For the 0cm air gap, the agreement between the TPS-calculated (RS-PB and RS-MC) and measured spot sizes were within ± 0.1mm. For the 35cm air gap, the RS-PB overpredicted spot sizes by 0.3-0.8mm, whereas the RS-MC computed spot sizes were within ± 0.3mm of measured spot sizes. In conclusion,spot size increment is dependent on the energy and air gap. The increase in spot size was more pronounced at lower energies ( < 150MeV) for all air gaps. The comparison between the TPS calculated and measured spot sizes showed that the RS-MC is more accurate (within ± 0.3mm), whereas the RS-PB overpredicted (up to 0.8mm) the spot sizes when a range shifter (7.5cm WET) and large air gaps are encountered in the proton beam path.

We investigate the uncertainty associated with the Fluorescence Recovery After Photobleaching, FRAP, which is widely used in the determination of diffusion coefficient for bio molecules. The uncertainty of our FRAP technique stems from the measurement of the spot size and the half time. The uncertainties of the FRAP is evaluated by considering the uncertainty propagation through the measurements of both spot size and the half time. Finally, we suggest an approach to estimate the effective diffusion coefficient by considering slip conditions between the fluorescent beads and the fluid. The diffusion coefficients measured by the FRAP is close to those obtained from the Stokes-Einstein relation together with the slip correction factor rather than that obtained solely by the Stokes-Einstein equation.

Purpose: To characterize the beam spot size of Siemens linear accelerators and assess its long‐term stability for megavoltage cone‐beam CT (MV‐CBCT) application. Method and Materials: A laminated beam spot camera of length 20 cm was constructed for the measurement of the beam spot size. With the linac gantry at 180°, the camera was positioned on the compensator tray and a Kodak XV film placed on it. An exposure was delivered using photon (6, 10, 18 MV) beams and the FWHM of the resulting source intensity profile used as a measure of the beam spot size. Measurement of the beam spot size was performed in both the gun‐target direction (in‐plane) and the cross‐plane direction for seven Siemens accelerators. To assess the long‐term stability of the beam spot size, measurements taken 1 year apart were compared to each other. Results: The measured beam spot diameters (FWHM) range from 1.6–2.8 mm. For all accelerators, the in‐plane spot size was equal to or larger than the corresponding cross‐plane spot size by up to 0.6 mm. Treatment units of the same design had spot sizes that were, in general, not identical but differed by up to 1 mm. Comparison of measurements on the Primus' and Mevatrons showed the introduction of the former (new generation accelerators) did not necessarily lead to a reduction in the spot size. Also, beam spot sizes measured 1 year apart were found to be similar. Conclusions: The new accelerator models did not in general provide an improvement in the spot size compared to the old models. Assessment of the long‐term stability of the beam spot showed the spot size remains fairly stable over time. However, the observed spot sizes are large in relation to focal spot size of diagnostic x‐ray imaging devices, and this might compromise MV‐CBCT image quality.

Study on laser spot size measurement by scanning-slit method based on back-injection interferometry

The quality of blood values analyzed from survey-collected dried blood spot (DBS) samples is affected by fieldwork conditions, particularly spot size. We offer an image-based algorithm that accurately measures the area of field-collected DBS and we investigate the impact of spot size on the analyzed blood marker values. SHARE, a pan-European study, collected 24 000 DBS samples in 12 countries in its sixth wave. Our new algorithm uses photographs of the DBS samples to calculate the number of pixels of the blood-covered area to measure the spot sizes accurately. We ran regression models to examine the association of spot size and seven DBS analytes. We then compared the application of our new spot-size measures to common spot-size estimation. Using automated spot-size measurement, we found that spot size has a significant effect on all markers. Smaller spots are associated with lower measured levels, except for HbA1c, for which we observe a negative effect. Our precisely measured spot sizes explain substantially more variance of DBS analytes compared to commonly used spot-size estimation. The new algorithm accurately measures the size of field-collected DBS in an automated way. This methodology can be applied to surveys even with very large numbers of observations. The measured spot sizes improve the accuracy of conversion formulae that translate blood marker values derived from DBS into venous blood values. The significance of the spot-size effects on biomarkers in DBS should also incentivize the improvement of fieldwork training and monitoring.

The key aspect of working with F-Theta lenses is the importance of working in the Back Focal Length (BFL) of the lens as defined by the manufacturer. Only at this point will there be optimal consistency in marking performance across the working plane. If one works outside of the BFL, even when the best available focus is achieved in the centre of the field, there will be an increased variance of the feature or spot size across the field. This variance is lowest for high quality low M2 beams which exhibit a high Rayleigh length and hence depth of focus. Working with higher M2 beams out of focus means that there will be significant variance over the field. Thus in order to achieve the finest and most consistent feature size desired, always work in the vendor specified BFL plane of the lens. Any change in spot size must then be accomplished by either changing the input diameter of the beam or changing focal length of the F-theta lens. Simply varying working distance to change spot size will result in an inconsistent marking across the field.Another important consideration is the state of collimation of the input beam from the laser to the scanner. If the beam is poorly collimated either diverging or converging this will affect the effective focal position of the beam and hence the working plane. Most consistent film ablation and dark (oxide) marks across a scan field require the collimation of the input beam to be adjusted so that the optimal focal condition corresponds with the specified BFL of the F-Theta lens being used.Attempting to use a system where the focus turns out to be even 1% from the specified BFL will change both spot size and will vary power density at different points in the mark field and in some cases even shift the focus.This study highlights the need to adjust the input of the beam into the scan head to focus at the specified BLF for the F-theta lens. Such adjustment allows users for example to fully benefit from advantages of higher powered, higher-mode lasers.The key aspect of working with F-Theta lenses is the importance of working in the Back Focal Length (BFL) of the lens as defined by the manufacturer. Only at this point will there be optimal consistency in marking performance across the working plane. If one works outside of the BFL, even when the best available focus is achieved in the centre of the field, there will be an increased variance of the feature or spot size across the field. This variance is lowest for high quality low M2 beams which exhibit a high Rayleigh length and hence depth of focus. Working with higher M2 beams out of focus means that there will be significant variance over the field. Thus in order to achieve the finest and most consistent feature size desired, always work in the vendor specified BFL plane of the lens. Any change in spot size must then be accomplished by either changing the input diameter of the beam or changing focal length of the F-theta lens. Simply varying working distance to change spot size will result in an inco...

An evaluation of the variation in focal plane position and spot size for a 1,650 W fast axial flow CO{sub 2} laser was performed. Multiple measurements of the focused beam were taken at stepped intervals along the beam axis to create a composite representation of the focus region. Measurements were made at several power levels from low to full power for each of five nominally identical lenses. It was found that as laser output power increases, the minimum focused spot radius increases, and the position of minimum focus shifts toward the laser resonator. These effects were attributed to observed variations in the diameter of the beam entering the focusing lens. For the ZnSe (f = 127 mm) lenses examined, variations in spot radius and focal plane position were seen. Lenses with high rated absorption had a larger variation in spot size and effective focal length than those with low absorption. Lenses that had previously been degraded by welding had the greatest variation.

The purpose of this study was to parametrize the in-air one sigma spot size for various energies and air gaps in pencil beam scanning (PBS) proton therapy. The current study included range shifters with a water equivalent thickness (WET) of 40mm (RS40) and 75mm (RS75). For RS40, the spot sizes were measured for energies ranging from 80 to 225MeV in increments of 2.5MeV, whereas the air gap was varied from 5 to 25cm in increments of 2.5cm. For RS75, the spot sizes were measured for energies ranging from 120 to 225MeV in increments of 2.5MeV, whereas the air gap was varied from 5 to 35cm in increments of 2.5cm. For both RS40 and RS75, all measurements (n = 1090) were acquired at the isocenter using a Lynx 2D scintillation detector. For RS40, the spot sizes increased from 3.1mm to 10.4mm, whereas the variation in spot sizes for RS75 ranged from 3.3mm to 13.1mm. For each range shifter, an analytical equation demonstrating the relationship of the spot size with the proton energy and air gap was obtained. The best parametrization results were obtained with the 3rd degree polynomial fits of the energy and air gap parameters. The average difference between the modeled and measured spot sizes was 0.0 ± 0.1mm (range, -0.24-0.21mm) for RS40, and 0.0 ± 0.1mm (range, -0.23-0.15mm) for RS75. In conclusion, the analytical model agrees within ± 0.25mm of the measured spot sizes on a ProteusPLUS PBS proton system with a PBS dedicated nozzle.

Motivation: Synthetic biology studies how to design and construct biological systems with functions that do not exist in nature. Biochemical networks, although easier to control, have been used less frequently than genetic networks as a base to build a synthetic system. To date, no clear engineering principles exist to design such cell-free biochemical networks.Results: We describe a methodology for the construction of synthetic biochemical networks based on three main steps: design, simulation and experimental validation. We developed BioNetCAD to help users to go through these steps. BioNetCAD allows designing abstract networks that can be implemented thanks to CompuBioTicDB, a database of parts for synthetic biology. BioNetCAD enables also simulations with the HSim software and the classical Ordinary Differential Equations (ODE). We demonstrate with a case study that BioNetCAD can rationalize and reduce further experimental validation during the construction of a biochemical network.Availability and implementation: BioNetCAD is freely available at http://www.sysdiag.cnrs.fr/BioNetCAD. It is implemented in Java and supported on MS Windows. CompuBioTicDB is freely accessible at http://compubiotic.sysdiag.cnrs.fr/Contact: stephanie.rialle@sysdiag.cnrs.fr; franck.molina@sysdiag.cnrs.frSupplementary information: Supplementary data are available at Bioinformatics online.

A novel reflective THz imaging objective mirror design is presented and characterized that can switch between pairs of numerical aperture and focal length while maintaining a fixed back focal distance (BFD). This allows the user to easily explore the effect of varying spot size, depth of field and working distance paremter during medical imaging studies without the need for optical realignment. The objective assembly design employs conjugate pairs of off axis parabolic (OAP) mirrors that accept and output parallel, collimated beams. Three pairs of effective focal length (EFL) mirrors were evaluated using a pulsed THz imaging system operating at an effective center frequency of 525 GHz with 125 GHz of 3 dB bandwidth. For the 25.4 mm 50.8 mm, and 76.2 mm EFL mirror pairs, the objective mirror design achieves a 10%–90% edge response measurements of 0.6 mm, 1.3 mm, and 2.1 mm and depth of field of 0.86 mm, 4.0 mm, and 11.7 mm, respectively. Investigation of the propagation of Gaussian THz beam profile from the photoconductive source, through the objective, and to the detector are presented. The knife-edge measurements agree with the predicted focused illumination spot size at the target and the predicted power at the detector focal plane, suggesting the entirety of focused THz beam profiles are effectively captured at the detector plane. Furthermore simulations show that the beam spot walks away from the detector aperture in the detection plane as the target plane is moved in and out of the system focal plane. This suggests that the system is operating in a regime that resembles confocal optical setup. Additionally, the off-axis distortion of field energy distribution and introduction of cross-polarization components is analyzed and the differences to optimal configurations analyzed. We conclude that the deviation of our systems optical setup from the optimal “ortho” conjugate configuration results in minimal degradation in optical performance. This suggests that OAP mirror setups can be designed to maximize practicality with marginal reductions in performance.

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.

High power single-mode fiber-lasers with CW output power 40 - 200 W was applied to microwelding. Thermal conduction equations of a square heat source were derived to calculate the temperature distribution and the mean temperature within the beam area. The penetration depth can be predicted assuming the beam-irradiation area is heated up to the boiling temperature of the material. High-speed photographs showed that a keyhole with the size of approximately focused beam spot is formed in the molten pool, of which diameter is in good agreement with the measured spot size. The humping defect can be suppressed by using fine beam spot size, because the width of the flow channel beside the keyhole is kept widely even at very high welding speeds rsulting in stable flow of the molten metal. Ultra-high speed welding up to a velocity of 1500 mm/s was attained without humping in SUS304 stainless steel foil. Sound lap welding of thin foils of <i>10 &mu;m</i> to <i>30 &mu;m</i> is demonstrated at welding speed of <i>920 mm/s</i>. Penetration welding of 800 &mu;m in thickness was achieved at laser power of 200 W.

Proton beam spot size and position measurements using a multi-strip ionization chamber

Image distortions during the propagation of optical beam in the turbulent atmosphere are provoked. Exposure time has effect on the space distribution characteristics of light image in the focal-plane CCD or CMOS sensor. The effect of exposure time on the spot size and shape is analyzed both theoretically and experimentally. The expression of spot size variable with exposure time has been developed from the angle-of-arrival fluctuation by the longitudinal and transverse components. In an optical free-space laser transmission experiment over a three-month period, measurements of spot size at variable exposure times are shown. Theoretical and experimental results illuminate the important point that the effect of exposure time must be considered for the optical design. The results show that the spot size decreases with exposure time increasing. A rapid decrease is showed in the spot size for short exposure times up to about 20msec.

The minimum spotsize, beam quality or M{sup 2}, and Strehl ratio of a focused laser beam provide different measures of the performance of the laser/optic system. Focusing lenses typically used to provide irradiances sufficient to cause melting and/or vaporization of metals or ceramics typically exhibit considerable spherical aberration, and thus limit the minimum spotsize attainable for a given lens at a specific laser power. The purpose of this work is to quantify the increase in the minimum spotsize and decrease in Strehl ratio of a focused materials processing CW Nd:YAG laser caused by laser cavity heating and spherical aberration introduced by the focusing lens. Minimum spotsize was determined by making several measurements of spotsize along the propagation direction using a scanning aperture system, and fitting the data to the laser propagation equation. These measurements were performed for 6 plano-convex lenses of different focal lengths, using laser powers ranging from 500 to 1500 watts. A nonlinear variation of spotsize with laser power and with focal length was observed for the lenses and power levels tested.