A new microscopic principle.
TL;DR: An improvement of the resolution by one decimal wotild require a correction of the objective to four decimals, a practically hopeless task.
Abstract: IT is known that the spherical aberration of electron lenses sets a limit to the resolving power of electron microscopes at about 5 A. Suggestions for the correction of objectives have been made ; but these are difficult in themselves, and the prospects of improvement are further aggravated by the fact that the resolution limit is proportional to the fourth root of the spherical aberration. Tnus an improvement of the resolution by one decimal wotild require a correction of the objective to four decimals, a practically hopeless task.
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2,002 citations
TL;DR: In this paper, a simplified scheme for phase-contrast imaging based on an X-ray source having high spatial (but essentially no chromatic) coherence is presented. But the method is not suitable for large areas of irradiation, and it can operate with a lower absorbed dose than traditional Xray imaging techniques, and should find broad application in clinical, biological and industrial settings.
Abstract: IN conventional radiography, X-rays which pass through an object along different paths are differentially absorbed, and the intensity pattern of the emerging beam records the distribution of absorbing materials within the sample. An alternative approach is phase-contrast radiography, which instead records variations of the phase of the emerging radiation. Such an approach offers improved contrast sensitivity, especially when imaging weakly absorbing samples. Unfortunately, current phase-contrast imaging techniques1–11 generally require highly monochromatic plane-wave radiation and sophisticated X-ray optics, so their use is greatly restricted. Here we describe and demonstrate a simplified scheme for phase-contrast imaging based on an X-ray source having high spatial (but essentially no chromatic) coherence. The method is compatible with conventional polychromatic micro-focus X-ray tube sources, is well suited to large areas of irradiation, can operate with a lower absorbed dose than traditional X-ray imaging techniques, and should find broad application in clinical, biological and industrial settings.
1,673 citations
TL;DR: This work demonstrates simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object and solves the twin‐image problem of in‐line holography and is capable of analysing data obtained using X‐ray microscope, electron microscopy, neutron microscopy or visible‐light microscopy.
Abstract: We demonstrate simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object. Subject to the assumptions explicitly stated in the derivation, the algorithm solves the twin-image problem of in-line holography and is capable of analysing data obtained using X-ray microscopy, electron microscopy, neutron microscopy or visible-light microscopy, especially as they relate to defocus and point projection methods. Our simple, robust, non-iterative and computationally efficient method is applied to data obtained using an X-ray phase contrast ultramicroscope.
1,589 citations
Cites background from "A new microscopic principle."
...…in this way, there are strong parallels with Gabor’s original conception of in-line holography, which ‘allows one to dispense altogether with ... objectives’ and instead works with ‘Micrographs [that] are obtained in a two-step process’, namely, recording followed by reconstruction (Gabor, 1948)....
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...objectives’ and instead works with ‘Micrographs [that] are obtained in a two-step process’, namely, recording followed by reconstruction (Gabor, 1948)....
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TL;DR: In this paper, a two-step imaging process is described from a communication-theory viewpoint, which consists of three well-known operations: a modulation, a frequency dispersion, and a square-law detection.
Abstract: A two-step imaging process discovered by Gabor involves photographing the Fresnel diffraction pattern of an object and using this recorded pattern, called a hologram, to construct an image of this object. Here, the process is described from a communication-theory viewpoint. It is shown that construction of the hologram constitutes a sequence of three well-known operations: a modulation, a frequency dispersion, and a square-law detection. In the reconstruction process, the inverse-frequency-dispersion operation is carried out. The process as normally carried out results in a reconstruction in which the signal-to-noise ratio is unity. Techniques which correct this shortcoming are described and experimentally tested. Generalized holograms are discussed, in which the hologram is other than a Fresnel diffraction pattern.
1,543 citations
TL;DR: In this paper, a widebandwidth three-dimensional holographic microwave imaging technique is described for the detection of concealed weapons or other contraband carried on personnel since millimeter-waves are nonionizing, readily penetrate common clothing material, and are reflected from the human body and any concealed items.
Abstract: Millimeter-wave imaging techniques and systems have been developed at the Pacific Northwest National Laboratory (PNNL), Richland, WA, for the detection of concealed weapons and contraband at airports and other secure locations. These techniques were derived from microwave holography techniques that utilize phase and amplitude information recorded over a two-dimensional aperture to reconstruct a focused image of the target. Millimeter-wave imaging is well suited for the detection of concealed weapons or other contraband carried on personnel since millimeter-waves are nonionizing, readily penetrate common clothing material, and are reflected from the human body and any concealed items. In this paper, a wide-bandwidth three-dimensional holographic microwave imaging technique is described. Practical weapon detection systems for airport or other high-throughput applications require high-speed scanning on the order of 3 to 10 s. To achieve this goal, a prototype imaging system utilizing a 27-33 GHz linear sequentially switched array and a high-speed linear scanner has been developed and tested. This system is described in detail along with numerous imaging results.
1,440 citations
Cites methods from "A new microscopic principle."
...Microwave holography is very similar to acoustic holography [6], [7] and both techniques are long-wavelength implementations of the original optical holography techniques developed by Gabor et al. [ 8 ], [9]....
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