A wavefront that passed through the system was confronted by alternate opaque and transparent regions, so that it underwent a modulation in amplitude. Earliest devices were multiple-slit assemblies, consisting of a grid of fine wire or thread wound about and extending between two parallel screws, which served as spacers. Joseph Fraunhofer first used diffraction gratings in 1819 to observe the spectrum of the sun. Applications are expanding one of the fastest growing areas for gratings-laser pulse compression-didn’t even exist until a few years ago. Gratings are indispensable in helping physicists determine the structure of atoms or helping astronomers calculate the chemical composition of stars and the rotation of galaxies. These minute, periodic structures diffract, or disperse, incident light in such a way that the individual wavelengths making up the incident light can be differentiated. Finally, improvements in this technology could provide an economical solution for aberration-corrected high-resolution STEM in certain use scenarios.Diffraction gratings are fundamental optical elements that have a precise pattern of grooves superimposed on them. Our GCOR enables us to record aberration-corrected high-resolution high-angle annular dark field (HAADF-) STEM images, although yet without advancement in probe current and resolution. In this work, we show a proof-of-principle experiment that demonstrates successful correction of the spherical aberration in STEM by means of such a grating corrector (GCOR). This holographic device is installed in the probe forming aperture of a conventional electron microscope and can be designed to remove more » arbitrarily complex aberrations from the electron's wave front. In this paper, we describe an alternative method to correct for the spherical aberration of the objective lens in scanning transmission electron microscopy (STEM) using a passive, nanofabricated diffractive optical element. This is made possible by precise arrangements of multipole electrodes and magnetic solenoids to compensate the aberrations inherent to any focusing element of an electron microscope. In the past 15 years, the advent of aberration correction technology in electron microscopy has enabled materials analysis on the atomic scale. The author discusses the history of VLS gratings, their present applications, and their potential in the future. Future prospects of VLS gratings as dispersing elements, wavefront correctors and beamsplitters appear promising. more » These include: (1) aberration-corrected normal incidence concave gratings for Seya-Namioka monochromators and optical de-multiplexers, (2) flat-field grazing incidence concave gratings for plasma diagnostics, (3) aberration-corrected grazing incidence plane gratings for space-borne spectrometers, (4) focusing grazing incidence plane grating for synchrotron radiation monochromators, and (5) wavefront generators for visible interferometry of optical surfaces (particularly aspheres). Such seemingly exotic gratings are no longer only a theoretical curiosity, but have been ruled and used in a wide variety of applications. In contrast, a varied line-space (VLS) grating, in common nomenclature, is a design in which the groove positions are relatively unconstrained yet possess sufficient symmetry to permit mechanical ruling. Conversely, the so-called ''holographic'' grating (formed by the interfering waves of coherent visible light), although severely constrained by the recording wavelength and recording geometry, has grooves which are typically neither equidistant, straight nor parallel. =, number = 1,Ī classically ruled diffraction grating consists of grooves which are equidistant, straight and parallel.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |