45 Matching Results

Search Results

Advanced search parameters have been applied.

How to construct a second-order achromat with a 90 degree phase advance

Description: The author shows how to construct a second order achromatic (T{sub ij6} = 0, i, j {element_of} {l_brace}1,2{r_brace}) beamline with a total phase advance of 450{degree} (360{degree} + 90{degree}). The goal is to construct a 90{degree} cell which is achromatic to second order. One possible way to do this is to construct a 360{degree} sector followed by a 90{degree} cell; put dipoles and sextupoles in the 360{degree} sector; and throw the aberrations into the 90{degree} cell such that the final transformation is achromatic. The author expresses the aberrations in the 360{degree} sector in terms of the 90{degree} cell and determine whether any combination of sextupoles gives the correct cancellation.
Date: July 5, 2000
Creator: Kobilarcik, T.
Partner: UNT Libraries Government Documents Department

Parametric-Resonance Ionization Cooling in Twin-Helix.

Description: Parametric-resonance Ionization Cooling (PIC) is proposed as the final 6D cooling stage of a highluminosity muon collider. For the implementation of PIC, we developed an epicyclic twin-helix channel with correlated optics. Wedge-shaped absorbers immediately followed by short rf cavities are placed into the twin-helix channel. Parametric resonances are induced in both planes using helical quadrupole harmonics. We demonstrate resonant dynamics and cooling with stochastic effects off using GEANT4/G4beamline. We illustrate compensation of spherical aberrations and benchmark COSY Infinity, a powerful tool for aberration analysis and compensation.
Date: September 1, 2011
Creator: V.S. Morozov, Ya.S. Derbenev, A. Afanasev, R.P. Johnson, Erdelyi. B., J.A. Maloney
Partner: UNT Libraries Government Documents Department

Spherical Aberration Corrections for the Electrostatic Gridded Lens

Description: Two methods of spherical aberration corrections of an electrostatic gridded lens have been studied with ray tracing simulations. Both methods are based on modifying electrostatic field on the periphery of the lens. In a simplest case such modification is done by extending the part of the grid support on its radial periphery in axial direction. In alternative method the electric field on the radial periphery of the lens is modified by applying an optimum voltage on an electrically isolated correcting electrode. It was demonstrated, that for a given focal length the voltage on this lens can be optimized for minimum aberration The performance of lenses is presented as a lens contribution to the beam RMS normalized emittance.
Date: May 1, 2008
Creator: Pikin,A.
Partner: UNT Libraries Government Documents Department

BETA-RAY SPECTROMETER WITH REDUCED SPHERICAL ABERRATION

Description: Modern {beta}-ray spectrometers are based upon the concept, first introduced by Svartholm and Siegbahn in 1946, of focusing in both the radial and vertical directions. The theory of axially symmetric devices has been carefully studied by a large number of workers, culminating in the analysis, in 1956, of Lee-Whiting and Taylor. These last authors calculate aberrations through the sixth order and show that by appropriate choice of the magnetic field a spectrometer can be designed with a relatively large transmission and a high resolution. The acceptable transmission is remarkable because the second-order 'spherical' aberration in the median plane of the image cannot be made to vanish identically, and consequently the design is forced to a tall thin aperture (or a slightly less advantageous short wide aperture) which a priori would seem to imply a low transmission. It is the purpose of this communication to show that if the arbitrary restriction to axially symmetric fields is removed, then both the radial and the vertical contributions to the 'spherical' aberration can be made to vanish in second order. That azimuthally varying field (AVF) afford the freedom to accomplish this end may well be suspected in view of the technological revolution that the concept has brought to other particle-handling devices.
Date: February 4, 1963
Creator: Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Spherical Focusing Mirror for the VUV-FEL

Description: Based on analysis and ray-tracing that he did, Jacek Krzywinski has suggested that it should be possible to focus the 32 nmVUV-FEL beam down below 0.2 {micro}m spot size with a normal-incidence multilayer-coated spherical mirror. There are advantages to a spherical mirror over an ellipsoid (or near-paraboloid) which are ease of manufacture and alignment. Off-axis aberrations are generally small, since for a beam that underfills the sphere's aperture, the beam itself defines the axis (rather than the optic). The dominant aberration for a sphere is spherical aberration, which decreases with increasing sphere radius of curvature. However, as the radius of curvature increases, so too does the focal length and f-number, and the diffraction-limited spot increases. Hence, as Jacek has pointed out, there is an optimum radius of curvature, to achieve the smallest possible spot, given a beam diameter. This optimum is determined by balancing the spread of the beam due to spherical aberration and the spread due to diffraction.
Date: September 20, 2005
Creator: Chapman, H N
Partner: UNT Libraries Government Documents Department

UCLA/FNPL Underdense Plasma Lens Experiment: Results and Analysis

Description: Focusing of a 15 MeV, 16 nC electron bunch by a gaussian underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated. The strong 1.9 cm focal length plasma lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Time resolved measurements of the focused electron bunch are also reported and compared to simulations.
Date: August 4, 2006
Creator: Thompson, M C; Badakov, H; Rosenzweig, J B; Travish, G; Fliller, R; Kazakevich, G M et al.
Partner: UNT Libraries Government Documents Department

Observations of underdense plasma lens focusing of relativistic electron beams

Description: Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion.
Date: June 1, 2007
Creator: Thompson, M. C.; Badakov, H.; Rosenzweig, J. B.; Travish, G.; Fliller, R.; Kazakevich, G. M. et al.
Partner: UNT Libraries Government Documents Department

LER control and mitigation: mask roughness induced LER

Description: In the push towards commercialization of extreme-ultraviolet lithography (EUVL), meeting the stringent requirements for line-edge roughness (LER) is increasingly challenging. For the 22-nm half-pitch node and below, the ITRS requires under 1.2 nm LER. Much of this LER is thought to arise from three significant contributors: LER on the mask absorber pattern, LER from the resist, and LER from mask roughness induced speckle. The physical mechanism behind the last contributor is becoming clearer, but how it is affected by the presence of aberrations is less well understood. Here, we conduct a full 2D aerial image simulation analysis of aberrations sensitivities of mask roughness induced LER for the first 37 fringe zernikes. These results serve as a guideline for future LER aberrations control. In examining how to mitigate mask roughness induced LER, we next consider an alternate illumination scheme whereby a traditional dipole's angular spectrum is extended in the direction parallel to the line-and-space mask absorber pattern to represent a 'strip'. While this illumination surprisingly provides merely minimal improvement to the LER as several alternate illumination schemes, overall imaging quality in terms of ILS, NILS, and contrast is improved. While the 22-nm half-pitch node can tolerate significant aberrations from a mask roughness induced LER perspective, total aberration levels for the 16-nm half-pitch node need to be strictly capped at 0.25nm rms to meet the ITRS guidelines. An individual aberrations study for the first 37 fringe zernikes on the 16-nm half-pitch node at the 0.25nm rms level reveals a sensitivity to various forms of spherical aberrations (Z9 & Z25) and quadrafoil (Z28) in particular, under conventional crosspole illumination ({sigma} = 0.10). Compared to conventional dipole or crosspole illuminations, an extended dipole 'strip' illumination scheme offers a way to mitigate mask roughness induced LER, while still maintaining high imaging quality for critical mask ...
Date: February 21, 2011
Creator: McClinton, Brittany & Naulleau, Patrick
Partner: UNT Libraries Government Documents Department

Aberration analysis calculations for synchrotron radiation beamline design

Description: The application of ray deviation calculations based on aberration coefficients for a single optical surface for the design of beamline optical systems is reviewed. A systematic development is presented which allows insight into which aberration may be causing the rays to deviate from perfect focus. A new development allowing analytical calculation of line shape is presented.
Date: September 1, 1997
Creator: McKinney, W.R.; Howells, M. & Padmore, H.A.
Partner: UNT Libraries Government Documents Department

Absolute wavefront measurements of high-energy laser beams in the Beamlet Demonstration Project for the National Ignition Facility

Description: The authors measure the absolute wavefront of Beamlet output pulses and actively correct for slowly varying aberrations present when the power amplifiers are not fired. Provision is also made for active precompensation of pump-induced amplifier aberrations.
Date: November 1, 1994
Creator: Salmon, J.T.; Bliss, E.S.; Kartz, M.W. & Van Wonterghem, B.M.
Partner: UNT Libraries Government Documents Department

EMITTANCE MEASUREMENTS WITH A PULSED POWER PHOTO INJECTOR.

Description: This paper describes measurements of beam spot size and emittance of electron beams from a pulsed power photo-injector operating at 150keV output energy. In these measurements, electron bunches with charge up to 20 pC were created by a 300 fs pulse duration Ti: Sapphire laser system illuminating a polished copper cathode. Images of the electron beam were captured at two locations downstream from a solenoid focusing magnet. The focal spot size was studied as a function of bunch charge and accelerating gradient. Beam waists down to 85 microns were obtained. The focal spot size was found to be dominated by spherical aberration at low beam charges, however the beam trajectory is in good agreement with simulation.
Date: May 12, 2003
Creator: SMEDLEY,J.; SRINIVASAN RAO,T.; TSANG,T.; FARRELL,J.P. & BATCHELOR,K.
Partner: UNT Libraries Government Documents Department

Correction of aberrations - past, present and future.

Description: The performance of static rotationally symmetric electron lenses is limited by unavoidable chromatic and spherical aberrations. In 1936, Scherzer demonstrated that the integrands of the integral expressions for the coefficients of these aberrations can be written as a sum of positive quadratic terms. Hence these coefficients can never change sign. This important result is called the Scherzer theorem, the only theorem existing in electron optics. Employing variational methods, Tretner determined the field of magnetic and electrostatic round lenses, which yields the smallest spherical aberration coefficient for particular constraints [2]. Unfortunately, these coefficients are still too large for realistic boundaries to enable sub-Angstrom resolution at medium voltages of about 200 to 300 kV. Therefore, the only possibility to directly reach this limit is the correction of the troublesome aberrations. It was again Scherzer who showed different procedures for canceling these aberrations [3]. The most promising is the incorporation of a corrector consisting of multipole elements or of a tetrode mirror in the case of low voltages. Although the mirror is rotationally symmetric, a non-rotationally symmetric beam splitter is needed to separate the incident beam from the reflected beam.
Date: February 21, 2002
Creator: Rose, H.
Partner: UNT Libraries Government Documents Department

High-resolution adaptive optics scanning laser ophthalmoscope with dual deformable mirrors for large aberration correction

Description: Scanning laser ophthalmoscopes with adaptive optics (AOSLO) have been shown previously to provide a noninvasive, cellular-scale view of the living human retina. However, the clinical utility of these systems has been limited by the available deformable mirror technology. In this paper, we demonstrate that the use of dual deformable mirrors can effectively compensate large aberrations in the human retina, making the AOSLO system a viable, non-invasive, high-resolution imaging tool for clinical diagnostics. We used a bimorph deformable mirror to correct low-order aberrations with relatively large amplitudes. The bimorph mirror is manufactured by Aoptix, Inc. with 37 elements and 18 {micro}m stroke in a 10 mm aperture. We used a MEMS deformable mirror to correct high-order aberrations with lower amplitudes. The MEMS mirror is manufactured by Boston Micromachine, Inc with 144 elements and 1.5 {micro}m stroke in a 3 mm aperture. We have achieved near diffraction-limited retina images using the dual deformable mirrors to correct large aberrations up to {+-} 3D of defocus and {+-} 3D of cylindrical aberrations with test subjects. This increases the range of spectacle corrections by the AO systems by a factor of 10, which is crucial for use in the clinical environment. This ability for large phase compensation can eliminate accurate refractive error fitting for the patients, which greatly improves the system ease of use and efficiency in the clinical environment.
Date: January 25, 2007
Creator: Chen, D; Jones, S M; Silva, D A & Olivier, S S
Partner: UNT Libraries Government Documents Department

Using geometric algebra to study optical aberrations

Description: This paper uses Geometric Algebra (GA) to study vector aberrations in optical systems with square and round pupils. GA is a new way to produce the classical optical aberration spot diagrams on the Gaussian image plane and surfaces near the Gaussian image plane. Spot diagrams of the third, fifth and seventh order aberrations for square and round pupils are developed to illustrate the theory.
Date: May 1, 1997
Creator: Hanlon, J. & Ziock, H.
Partner: UNT Libraries Government Documents Department

Aberration correction for analytical in situ TEM - the NTEAM concept.

Description: Future aberration corrected transmission electron microscopes (TEM) will have a strong impact in materials science, since such microscopes yield information on chemical bonding and structure of interfaces, grain boundaries and lattice defects at an atomic level. Beyond this aberration correction offers new possibilities for in situ experiments performed under controlled temperature, magnetic field, strain etc. at atomic resolution. Such investigations are necessary for solving problems arising from electronic component miniaturization, for example. Significant progress can be expected by means of analytical aberration corrected TEM. These next generation microscopes will be equipped with an aberration corrected imaging system, a monochromator and aberration corrected energy filters. These novel elements have already been designed and partially realized [1,2,3].
Date: March 5, 2002
Creator: Kabius, B.; Allen, C. W. & Miller, D. J.
Partner: UNT Libraries Government Documents Department

Lens designs for high irradiance application of multi-kilowatt Nd:YAG welding lasers

Description: Multi-kilowatt Nd:YAG lasers provide an appealing solution for aluminum laser welding applications due to increased bulk absorption and ease of beam delivery as compared to high power CO{sub 2} laser systems. However, high numerical aperture optics are required to overcome the relatively poor beam quality associated with these lasers and to achieve a high irradiance. Several lens designs have been developed and evaluated to achieve the high irradiance values required to provide good coupling into aluminum alloys. The results of these tests demonstrate that near diffraction limited performance can be achieved for high numerical aperture elements. Additionally, an inverse-telephoto lens design has been developed and characterized to further demonstrate the feasibility of producing a high irradiance with a functional working distance from the weld surface.
Date: April 1, 1996
Creator: Keicher, D.M. & Essien, M.
Partner: UNT Libraries Government Documents Department

Spotsize measurements of a focused CW Nd:YAG laser

Description: 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.
Date: March 1, 1995
Creator: Essien, M.; Schanwald, L.P. & Fuerschbach, P.W.
Partner: UNT Libraries Government Documents Department

Hexagonal close-packed arrays of optical fibers for partitioning a laser beam into individual beamlets: Analysis and prototype fabrication

Description: Hexagonally close-packed arrays of optical fibers were investigated for partitioning a laser beam into individual beamlets for distribution to remote and variously located regions for experimental purposes. Equations were derived giving the efficiency of coupling the laser beam into the fibers as a function of the fiber cross section geometry and the number of fibers in a given hexagonal array, assuming that the laser beam just filled the outermost fibers in the array. The analysis was done also for the case in which a small lens was used in conjunction with each fiber in the array. For the lens fiber combination, the effect of spherical aberration was calculated and equations were derived giving the location and radius of the so-called circle of least confusion as a function of the lens geometry. The effects of aberration were also compared with the calculated diffraction limited focal spot size for a lens in the array. The effect of misalignment of a lens relative to the laser beam was analyzed with regard to the efficiency of energy coupled into the mating fiber. A prototype array was fabricated utilizing a hexagonal array of 61 fibers.
Date: July 1, 1997
Creator: Klingsporn, P.E.
Partner: UNT Libraries Government Documents Department

Comparison of four methods of interferogram reduction and interpretation

Description: This paper will address the problem of accurate reduction and interpretation of interferograms. Peak-to-valley wavefront deformation will be the main criterion of evaluation. Interferograms containing power, spherical aberration, coma, and astigmatism will be evaluated using four different methods. These methods will be (1) visual interpretation using a ''harp,'' (2) manual interpretation, (3) automatic digitization (Zygo Zapp), and (4) computer interpretation (fringe). The strengths and weaknesses of these methods, including cost, time, accuracy, and repeatability, will be discussed. Reference will be made to ''Optical Interferograms-Reduction and Interpretation'' an ASTM publication. 2 refs., 5 figs.
Date: January 1, 1985
Creator: Woodfin, G. & Feind, M.
Partner: UNT Libraries Government Documents Department

Global coordinates and exact aberration calculations applied to physical optics modeling of complex optical systems

Description: Historically, wave optics computer codes have been paraxial in nature. Folded systems could be modeled by ''unfolding'' the optical system. Calculation of optical aberrations is, in general, left for the analyst to do with off-line codes. While such paraxial codes were adequate for the simpler systems being studied 10 years ago, current problems such as phased arrays, ring resonators, coupled resonators, and grazing incidents optics require a major advance in analytical capability. This paper describes extension of the physical optics codes GLAD and GLAD V to include a global coordinate system and exact ray aberration calculations. The global coordinate system allows components to be positioned and rotated arbitrarily. Exact aberrations are calculated for components in aligned or misaligned configurations by using ray tracing to compute optical path differences and diffraction propagation. Optical path lengths between components and beam rotations in complex mirror systems are calculated accurately so that coherent interactions in phased arrays and coupled devices may be treated correctly.
Date: January 1, 1986
Creator: Lawrence, G.; Barnard, C. & Viswanathan, V.K.
Partner: UNT Libraries Government Documents Department

Monochromator systems. Lecture 3

Description: General properties of monochromators are discussed, and some useful formulas are given for optical design. Only the Rowland reflection grating, whose groove pattern consists of the intersection of the substrate surface with a set of parallel equispaced planes, is considered. The focusing properties of a toroidal grating are discussed. Some aberrations are briefly described, and quantitative calculations of the aberrations are considered. Dispersion, resolution, and phase space acceptance are discussed. (LEW)
Date: December 1, 1985
Creator: Howells, M.R.
Partner: UNT Libraries Government Documents Department

Correction of the Chromaticity up to Second Order for MEIC

Description: The proposed electron collider lattice exhibits low β- functions at the Interaction Point (IP) (βx∗100mm − βy∗ 20 mm) and rather large equilibrium momentum spread of the collider ring (δp/p = 0.00158). Both features make the chromatic corrections of paramount importance. Here the chromatic effects of the final focus quadruples are cor- rected both locally and globally. Local correction features symmetric sextupole families around the IP, the betatron phase advances from the IP to the sextupoles are chosen to eliminate the second order chromatic aberration. Global interleaved families of sextupoles are placed in the figure-8 arc sections, and non-interleaved families at straight sec- tion making use of the freely propagated dispersion wave from the arcs. This strategy minimizes the required sex- tupole strength and eventually leads to larger dynamic aper- ture of the collider. The resulting spherical aberrations induced by the sextupoles are mitigated by design; the straight and arc sections optics features an inverse identity transformation between sextupoles in each pair.
Date: March 1, 2010
Creator: H. K. Sayed, S.A. Bogacz, P. Chevtsov
Partner: UNT Libraries Government Documents Department

Ion optics of RHIC EBIS

Description: RHIC EBIS has been commissioned to operate as a versatile ion source on RHIC injection facility supplying ion species from He to Au for Booster. Except for light gaseous elements RHIC EBIS employs ion injection from several external primary ion sources. With electrostatic optics fast switching from one ion species to another can be done on a pulse to pulse mode. The design of an ion optical structure and the results of simulations for different ion species are presented. In the choice of optical elements special attention was paid to spherical aberrations for high-current space charge dominated ion beams. The combination of a gridded lens and a magnet lens in LEBT provides flexibility of optical control for a wide range of ion species to satisfy acceptance parameters of RFQ. The results of ion transmission measurements are presented.
Date: September 10, 2011
Creator: Pikin, A.; Alessi, J.; Beebe, E.; Kponou, A.; Okamura, M.; Raparia, D. et al.
Partner: UNT Libraries Government Documents Department

FY 2006 Miniature Spherical Retroreflectors Final Report

Description: Research done by the Infrared Photonics team at Pacific Northwest National Laboratory (PNNL) is focused on developing miniature spherical retroreflectors using the unique optical and material properties of chalcogenide glass to reduce both performance limiting spherical aberrations. The optimized optical performance will provide efficient signal retroreflection that enables a broad range of remote detection scenarios for mid-wave infrared (MWIR) and long-wave infrared (LWIR) sensing applications. Miniature spherical retroreflectors can be developed to aid in the detection of signatures of nuclear proliferation or other chemical vapor or radiation signatures. Miniature spherical retroreflectors are not only well suited to traditional LIDAR methods for chemical plume detection and identification, but could enable remote detection of difficult semi-volatile chemical materials or low level radiation sources.
Date: December 28, 2006
Creator: Anheier, Norman C.; Bernacki, Bruce E. & Krishnaswami, Kannan
Partner: UNT Libraries Government Documents Department