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The success of the phase-contrast microscope has led to a number of subsequent phase-imaging methods. In 1952, Georges Nomarski patented what is today known as differential interference contrast (DIC) microscopy. [8] It enhances contrast by creating artificial shadows, as if the object is illuminated from the side.
The advantages of these methods compared to normal absorption-contrast X-ray imaging is higher contrast for low-absorbing materials (because phase shift is a different mechanism than absorption) and a contrast-to-noise relationship that increases with spatial frequency (because many phase-contrast techniques detect the first or second ...
The passage of many pairs of rays through pairs of adjacent points in the sample (and their absorbance, refraction and scattering by the sample) means an image of the sample will now be carried by both the 0° and 90° polarised light. These, if looked at individually, would be bright field images of the sample, slightly offset from each other ...
The effect of the contrast transfer function can be seen in the alternating light and dark rings (Thon rings), which show the relation between contrast and spatial frequency. The contrast transfer function (CTF) mathematically describes how aberrations in a transmission electron microscope (TEM) modify the image of a sample.
Often the contrast reduction is of most interest and the translation of the pattern can be ignored. The relative contrast is given by the absolute value of the optical transfer function, a function commonly referred to as the modulation transfer function (MTF). Its values indicate how much of the object's contrast is captured in the image as a ...
The contrast between two adjacent areas in a TEM image can be defined as the difference in the electron densities in image plane. Due to the scattering of the incident beam by the sample, the amplitude and phase of the electron wave change, which results in amplitude contrast and phase contrast, correspondingly. Most images have both contrast ...
[20] [21] Quantitative phase-contrast microscopy has an advantage over fluorescent and phase-contrast microscopy in that it is both non-invasive and quantitative in its nature. Due to the narrow focal depth of conventional microscopy, live-cell imaging is to a large extent currently limited to observing cells on a single plane.