Measurement of the full complex degree of coherence using Fresnel diffraction from a phase discontinuity

2020 ◽  
Vol 45 (13) ◽  
pp. 3737
Author(s):  
Helia Hooshmand-Ziafi ◽  
Masoomeh Dashtdar ◽  
Khosrow Hassani
Keyword(s):  
Fresnel Diffraction ◽  
Degree Of Coherence ◽  
Phase Discontinuity

Observation of Phase Contrast Images in STEM and CTEM Modes by Using 100 kV Field Emission Electron Gun

1974 ◽  
Vol 32 ◽  
pp. 390-391
Author(s):  
Y. Harada ◽  
T. Goto ◽  
H. Koike ◽  
T. Someya
Keyword(s):  
Field Emission ◽  
Phase Contrast ◽  
Image Formation ◽  
Fresnel Diffraction ◽  
Experimental Results ◽  
Electron Gun ◽  
Scanning Microscopy ◽  
Emission Electron ◽  
Lattice Images

Since phase contrasts of STEM images, that is, Fresnel diffraction fringes or lattice images, manifest themselves in field emission scanning microscopy, the mechanism for image formation in the STEM mode has been investigated and compared with that in CTEM mode, resulting in the theory of reciprocity. It reveals that contrast in STEM images exhibits the same properties as contrast in CTEM images. However, it appears that the validity of the reciprocity theory, especially on the details of phase contrast, has not yet been fully proven by the experiments. In this work, we shall investigate the phase contrast images obtained in both the STEM and CTEM modes of a field emission microscope (100kV), and evaluate the validity of the reciprocity theory by comparing the experimental results.

Simulation of high-resolution annular dark field STEM images

1995 ◽  
Vol 53 ◽  
pp. 40-41
Author(s):  
E. J. Kirkland
Keyword(s):  
Electron Beam ◽  
Atomic Layer ◽  
Fresnel Diffraction ◽  
Dark Field ◽  
Objective Lens ◽  
Image Simulation ◽  
Small Probe ◽  
Annular Dark Field ◽  
Stem Image ◽  
Uniform Plane

In a STEM an electron beam is focused into a small probe on the specimen. This probe is raster scanned across the specimen to form an image from the electrons transmitted through the specimen. The objective lens is positioned before the specimen instead of after the specimen as in a CTEM. Because the probe is focused and scanned before the specimen, accurate annular dark field (ADF) STEM image simulation is more difficult than CTEM simulation. Instead of an incident uniform plane wave, ADF-STEM simulation starts with a probe wavefunction focused at a specified position on the specimen. The wavefunction is then propagated through the specimen one atomic layer (or slice) at a time with Fresnel diffraction between slices using the multislice method. After passing through the specimen the wavefunction is diffracted onto the detector. The ADF signal for one position of the probe is formed by integrating all electrons scattered outside of an inner angle large compared with the objective aperture.

Fresnel diffraction by a Round aperture

1970 ◽  
Vol 102 (12) ◽  
pp. 655-656
Author(s):  
L.I. Vidro ◽  
Yu.P. Basharov ◽  
A.E. Kudryashov
Keyword(s):  
Fresnel Diffraction

scholarly journals Measurement of the diffusion coefficient in liquids using Fresnel diffraction from a phase step

2021 ◽  
Vol 127 (8) ◽  
Author(s):  
Ahad Saber ◽  
Mohammad Taghi Tavassoly ◽  
Rasoul Aalipour
Keyword(s):  
Diffusion Coefficient ◽  
Fresnel Diffraction ◽  
Phase Step

scholarly journals Metalens Eyepiece for 3D Holographic Near-Eye Display

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1920
Author(s):  
Chang Wang ◽  
Zeqing Yu ◽  
Qiangbo Zhang ◽  
Yan Sun ◽  
Chenning Tao ◽  
...  
Keyword(s):  
Light Field ◽  
Three Dimensional ◽  
Fresnel Diffraction ◽  
Virtual Image ◽  
Display Devices ◽  
Computer Generated Holography ◽  
Wavefront Shaping ◽  
3D Scene ◽  
Optimum Solution ◽  
532 Nm

Near-eye display (NED) systems for virtual reality (VR) and augmented reality (AR) have been rapidly developing; however, the widespread use of VR/AR devices is hindered by the bulky refractive and diffractive elements in the complicated optical system as well as the visual discomfort caused by excessive binocular parallax and accommodation-convergence conflict. To address these problems, an NED system combining a 5 mm diameter metalens eyepiece and a three-dimensional (3D), computer-generated holography (CGH) based on Fresnel diffraction is proposed in this paper. Metalenses have been extensively studied for their extraordinary capabilities at wavefront shaping at a subwavelength scale, their ultrathin compactness, and their significant advantages over conventional lenses. Thus, the introduction of the metalens eyepiece is likely to reduce the issue of bulkiness in NED systems. Furthermore, CGH has typically been regarded as the optimum solution for 3D displays to overcome limitations of binocular systems, since it can restore the whole light field of the target 3D scene. Experiments are carried out for this design, where a 5 mm diameter metalens eyepiece composed of silicon nitride anisotropic nanofins is fabricated with diffraction efficiency and field of view for a 532 nm incidence of 15.7% and 31°, respectively. Furthermore, a novel partitioned Fresnel diffraction and resample method is applied to simulate the wave propagations needed to produce the hologram, with the metalens capable of transforming the reconstructed 3D image into a virtual image for the NED. Our work combining metalens and CGH may pave the way for portable optical display devices in the future.

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