How I Discovered Phase Contrast

Zernike, F.

doi:10.1126/science.121.3141.345

Cited by 673 publications

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“…In this case, the effect of spatial variations in specimen structure is imprinted only on the phase of the transmitted wave. As was eloquently explained by Zernike, perfect images of such objects show no contrast [1]. As a result, weak phase objects must be intentionally viewed in an out-of-focus condition in order to partially convert the phase modulation into an intensity modulation.…”

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Design of a microfabricated, two-electrode phase-contrast element suitable for electron microscopy

et al. 2007

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A miniature electrostatic element has been designed to selectively apply a ninetydegree phase shift to the unscattered beam in the back focal plane of the objective lens, in order to realize Zernike-type, in-focus phase contrast in an electron microscope. The design involves a cylindrically shaped, biased-voltage electrode, which is surrounded by a concentric grounded electrode. Electrostatic calculations have been used to determine that the fringing fields in the region of the scattered electron beams will cause a negligible phase shift as long as the ratio of electrode length to the transverse feature-size is greater than 5:1. Unlike the planar, three-electrode einzel lens originally proposed by Boersch for the same purpose, this new design does not require insulating layers to separate the biased and grounded electrodes, and it can thus be produced by a very simple microfabrication process. Scanning electron microscope images confirm that mechanically robust devices with feature sizes of ~1 µm can be easily fabricated. Preliminary experimental images demonstrate that these devices do apply a 90-degree phase shift between the scattered and unscattered electrons, as expected. Powerful though modern electron microscopes have become, they still remain relatively poor instruments for imaging thin, unstained biological specimens. Such specimens are weakly-scattering "phase objects", which is to say that the intensity of the transmitted electron beam remains virtually equal to that of the incident electron beam. In this case, the effect of spatial variations in specimen structure is imprinted only on the phase of the transmitted wave. As was eloquently explained by Zernike, perfect images of such objects show no contrast [1]. As a result, weak phase objects must be intentionally viewed in an out-of-focus condition in order to partially convert the phase modulation into an intensity modulation. of 23The use of objective-lens defocus (and, at higher resolution, spherical aberration as well) is an imperfect way to produce phase contrast in images of biological macromolecules. The problem with that "simple" approach is that such phase shifts vary continuously over the spectrum of spatial frequencies. While the contrast transfer function produced as the result of an optimal trade-off between the phase distortion due to defocus and that due to spherical aberration can approximate the desired value of 1 over a relatively broad range of spatial frequencies [2], this band of high contrast is limited to rather high-resolution features of the image. Since it is necessary to have substantial contrast at low resolution in order to see biological macromolecules, however, it is often necessary to use a much larger amount of defocus. Unfortunately, when a high enough amount of defocus is used to generate contrast on the size scale of individual macromolecules, the phase shifts produced at high resolution can be many times the desired value of /2. As a result, the contrast transfer function then oscillates multiple times in ...

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Design of a microfabricated, two-electrode phase-contrast element suitable for electron microscopy

et al. 2007

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“…However, if an additional phase difference is created between the undeviated (low spatial frequencies) and deviated (high spatial frequencies) light, then they interfere either constructively or destructively (depending on the amount of phase added) thereby converting the phase variation into amplitude contrast. Phase contrast imaging was developed in 1933 by Zernike [39] to observe phase objects. He used a phase plate to create a π/2 phase difference between the undeviated light and the light diffracted by the object thereby transforming minute variations in phase of the object into corresponding changes in the image contrast.…”

Section: Phase Contrast Imaging Of Biological Specimensmentioning

confidence: 99%

Optical Fourier techniques for medical image processing and phase contrast imaging

Yelleswarapu

Kothapalli

Rao

2008

Optics Communications

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This paper briefly reviews the basics of optical Fourier techniques (OFT) and applications for medical image processing as well as phase contrast imaging of live biological specimens. Enhancement of microcalcifications in a mammogram for early diagnosis of breast cancer is the main focus. Various spatial filtering techniques such as conventional 4f filtering using a spatial mask, photoinduced polarization rotation in photosensitive materials, Fourier holography, and nonlinear transmission characteristics of optical materials are discussed for processing mammograms. We also reviewed how the intensity dependent refractive index can be exploited as a phase filter for phase contrast imaging with a coherent source. This novel approach represents a significant advance in phase contrast microscopy.

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“…1 has its roots in the phase-contrast technique developed by Frits Zernike during the 1930s (for which he was later awarded a Nobel Prize in physics) (Zernike, 1955;Ferwerda, 1994;Goodman, 1996). Fig.…”

Section: High-resolution Wave-front Control Systemmentioning

confidence: 99%

Analysis of a high-resolution optical wave-front control system

2004

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We consider the formulation and analysis of a problem of automatic control: correcting for the distortion induced in an optical wave front due to propagation through a turbulent atmosphere. It has recently been demonstrated that high-resolution optical wave-front distortion suppression can be achieved using feedback systems based on high-resolution spatial light modulators and phase-contrast techniques. We examine the modeling and analysis of such adaptive optic systems, and show that under certain conditions, the nonlinear dynamical system models obtained are gradient systems (with energy functions that also serve as Lyapunov functions). These gradient systems (employing ÿxed phase-contrast sensors) serve as a starting point for understanding the design of practical high-resolution wave-front correction systems, in which the phase-contrast sensor itself is subject to control. ?

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How I Discovered Phase Contrast

Cited by 673 publications

References 0 publications

Design of a microfabricated, two-electrode phase-contrast element suitable for electron microscopy

Design of a microfabricated, two-electrode phase-contrast element suitable for electron microscopy

Optical Fourier techniques for medical image processing and phase contrast imaging

Analysis of a high-resolution optical wave-front control system

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