Phase-contrast microscopy

Phase-contrast microscopy converts differences in the phase of light passing through a specimen into brightness differences. It reveals transparent structures without staining them.

Phase shift: A change in the phase of a wave relative to a reference wave. Light slows and shifts phase as it passes through regions of differing thickness or refractive index.
Live-cell imaging: The observation of living cells over time using imaging methods that limit damage and disruption. Phase contrast reveals cell structure without requiring fixation or staining.
Bright-field microscopy: Light microscopy in which image contrast mainly comes from light absorbed or scattered by a specimen. Transparent unstained specimens often appear faint in bright field but distinct in phase contrast.
Frits Zernike: A Dutch physicist who developed phase-contrast microscopy and received the 1953 Nobel Prize in Physics. Zernike devised the method and its optical components.
Annular diaphragm: A ring-shaped aperture that produces a hollow cone of illumination in a microscope. It creates the illumination geometry required by the phase-contrast condenser.
Cell culture: The growth of cells outside an organism under controlled laboratory conditions. Phase contrast is routinely used to inspect cultured cells without disturbing them.
Differential interference contrast microscopy: A microscopy method that converts optical path gradients into contrast using polarized light and shearing prisms. It also images transparent specimens but produces a directional, relief-like appearance.
Nobel Prize in Physics 1953: The 1953 Nobel Prize in Physics, awarded to Frits Zernike for his phase-contrast method. The prize recognized the value of making transparent microscopic objects visible.
Phase plate: An optical element that changes the phase or amplitude of selected portions of a light wave. Placed in the objective's back focal plane, it shifts direct light relative to diffracted light.
Cell division: The process by which a cell produces daughter cells through division of its contents. Unstained mitotic cells can be followed as they change shape and divide.

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