Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Apparatus for measuring optical system coupling performance

Abstract: PROBLEM TO BE SOLVED: To evaluate the focusing performance of an a focal optical system in a suitable measuring direction by eliminating the skill of the measurement, improving the operability and measuring the worst direction of an image. SOLUTION: Pinholes P1 to P5 corresponding to the positions of a plurality of image heights of a lens 17 to be detected are formed at a pinhole plate 16, and uniformly illuminated from an entire light source 15. The plate 16 is moved in an optical axis direction at an X stage 21. Pinhole images (image surface 18 via the lens 17 is detected by CCD area sensors 41, and contrast transfer function MTF is calculated by Fourier transformation by a signal processing system 20. The system 20 detects the peak positions from the output signals of the pinhole images detected by the sensors 41 to 45, and calculates the peak positions by the Fourier transformed MTF based on the output section of the tangential T direction and radial R direction for passing the peak positions. It also calculates the MTF by the transformation based on the output section of the maximum deviating direction of the images detected by sensors 41 to 45, and evaluates the focusing performance of an afocal optical system at the image height.

Nanoscale x-ray holo-tomography of human brain tissue with phase retrieval based on multiphoton energy recordings

Abstract: X-ray cone-beam holo-tomography of unstained tissue from the human central nervous system reveals details down to sub-cellular length scales.1 This visualization of variations in the electron density of the sample is based on phase contrast techniques using intensities formed by self-interference of the beam between object and detector. Phase retrieval inverts diffraction and overcomes the phase problem by constraints such as several measurements at different Fresnel numbers for a single projection. Therefore, the object-to-detector distance (defocus) can be varied. However, for cone beam geometry, changing defocus changes magnification, which can be problematic in view of image processing and resolution. Alternatively, the photon energy can be altered (multi-E). Far from absorption edges, multi-E data yield the wavelength independent electron density. In this contribution we present multi-E holo-tomography at the GINIX setup of the P10 beamline at DESY. The instrument is based on a combined optics of elliptical mirrors and an x-ray waveguide positioned in the focal plane for further coherence, spatial Filtering and high numerical aperture.2 Previous results showed the suitability of this instrument for nanoscale tomography of unstained brain tissue.1 We demonstrate that upon energy variation, the focal spot is stable enough for imaging. To this end, a double crystal monochromator and automated alignment routines are required. Three tomograms of human brain tissue were recorded and jointly analyzed using phase retrieval based on the contrast transfer function formalism generalized to multiple photon energies. Variations of the electron density of the sample are successfully reconstructed.

High contrast measurement of nanoparticle with polarization interferometric nonlinear confocal microscope

Abstract: Polarization interferometric nonlinear confocal microscope has been developed to observe a submicron size object in high contrast. The microscope succeeded in resolving the inside of a 200-nm-diameter polymeric nanoparticle. According to CTF (contrast transfer function) measurement and three-dimensional imaging with the microscope, the best spatial resolution for the microscope is 10 nm.

An aberration corrected photoemission electron micorscope at the advanced light source

Abstract: An Aberration Corrected Photoemission Electron Microscope at the Advanced Light Source J. Feng 1 , A.A.MacDowell 1 , R.Duarte 1 , A.Doran 1 , E.Forest 2 , N.Kelez 1 , M.Marcus 1 , D.Munson 1 , H.Padmore 1 , K.Petermann 1 , S.Raoux 3 , D.Robin 1 , A.Scholl 1 , R.Schlueter 1 , P.Schmid 1 ,J. Stohr 4 , W.Wan 1 , D.H.Wei 5 and Y.Wu 6 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0810, Japan IBM, Almaden Research Center, 650 Harry Road, San Jose, CA 95120 USA Stanford Synchrotron Radiation Laboratory, P.O.Box 20450, Stanford, CA 94309, USA SRRC, No.1 R &D Rd. VI, Hsinchu 300, Taiwan Department of Physics, Duke University, Durham, NC 27708, USA Abstract. Design of a new aberration corrected Photoemission electron microscope PEEM3 at the Advanced Light Source is outlined. PEEM3 will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. The models to calculate the optical properties of the electron mirror are discussed. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system (50 nm) and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further. INTRODUCTION X-ray excited photoemission electron microscope (PEEM) combines the power of modern synchrotron radiation absorption spectroscopy with direct full imaging capability of PEEM. A conventional PEEM system consists of round lenses whose resolution is limited by spherical and chromatic aberration, and the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc always being positive [1]. As a result aberrations can only be minimized by adjusting the geometry of the electrodes but not eliminated. These aberrations limit the ultimate resolution, defined by a 50% value of the Modulation Transfer Function to be typically 50 – 100 nm, for x-ray illumination and a 20 KV extraction field [2]. Aberrations must be compensated in order to remove their deleterious effects on the imaging properties of the microscope. An electron mirror can have aberration coefficients of opposite sign but equal magnitude with respect to those of electron round lens so that in principle, the aberrations can be canceled out and the resolution can be improved ultimately to the diffraction limit. A new X-ray PEEM with an electron mirror aberration corrector at the ALS has been designed (PEEM3) and the overall layout and correction scheme are described. PEEM3 SYSTEM An elliptically polarized undulator (EPU) at the straight sector 11 of the ALS will be used to produce linearly polarized light of arbitrary azimuth and left and right handed circularly polarized radiation with continuous change of ellipticity. A variable line space (VLS) plane grating monochromator beamline will provide soft x-ray in the spectral range from 100eV to 1500eV. A VLS design was chosen as it gives the opportunity to dynamically measure the photon energy, by active monitoring of the position of the zero order beam with respect to that of the monochromatic light defined by the exit slit. This is of crucial importance in minimizing noise in x-ray dichroism

In situ correction of the spherical aberration in a double-toroidal electron analyzer.

Abstract: In an energy-dispersive electron spectrometer, the electrons with the same kinetic energy but different polar angles fly along different paths and impinge upon the detector at different locations. This behavior materializes the spherical aberration of the electron optics, which deteriorates the focussing quality on the detector, and thus the energy resolution of the instrument. Here, we demonstrate that, in general, the electron time of flight changes monotonically as a function of the polar angle. Combining the impact position on the detector and the time of flight of electrons, the spherical aberration can be corrected and the energy resolution can be significantly improved, 1.5× in the case of our double toroidal analyser. This correction method has a general applicability and can be of interest to experimentalists willing to push further the performances of their electron spectrometers when the time of flight is available.