charge-coupled device (CCD)
A small photoelectronic imaging device (typically 1.5 cm square) made from
a crystal of silicon in which numerous (at least 250,000) individual light-sensitive
picture elements (pixels) have been fabricated. Each pixel (less than 0.03
mm in size) is capable of storing electronic charges created by the absorption
of light. The name derives from the method of extracting the locally stored
charges from each pixel, which is done by transferring or "coupling" charges
from one pixel to the next by the controlled collapse and growth of adjacent
storage sites or potential wells. Each well is formed inside the silicon
crystal by the electric field generated by voltages applied to tiny, semi-transparent
metallic electrodes on the CCD surface. CCDs, placed at the receiving end
of telescopes to take pictures of very faint astronomical objects, have
almost completely superceded photographic plates for professional use. A
CCD spectrometer is an instrument that uses a modified CCD to obtain
images and spectra of X-ray sources.
Related category
• TELESCOPE
EQUIPMENT AND TECHNIQUES
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