Detector Arrays

During the past few decades, infrared astronomy has become a major field of science due to rapid advances in infrared detector technology. Many of these advances arose from U.S Department of Defense research into infrared array technology in the 1980's. Infrared radiation, having longer wavelengths and lower energy than visible light, does not have enough energy to interact with the photographic plates which are often used in visible light astronomy. Instead, infrared astronomers rely on electronic devices, to detect radiation. Infrared detectors use infrared-sensitive materials, made from alloys of exotic metallic substances, such as indium, antimony, silicon, mercury, cadmium, germanium, and tellurium. When infrared radiation falls on an infrared detector, the electrical resistance of the detector changes. This change in resistance is then measured and is related to the amount of infrared radiation falling on the detector. Since infrared detectors are extremely sensitive to heat, they must be kept in an environment which is as cold as possible. This is done through the use of cryogens such as liquid helium or nitrogen.

The development of infrared detector arrays in the 1980's, caused a giant leap in the sensitivity of infrared observations. Basically, a detector array is a combination of several individual detectors arranged in a lattice-like array. The individual detectors in an array are often called pixels - short for picture elements. These pixel arrays convert energy from infrared radiation into electrical signals, which are then converted into "bits" of digital data. In 1983 the IRAS mission used an array of 62 detectors. Astronomers now commonly use 256 x 256 arrays (thats 65,536 detectors!). Infrared detector technology continues to advance at a rapid rate. As a result, infrared astronomy has developed more rapidly than any other field of astronomy and continues to bring us exciting new views of the universe.

Detector array for the Spitzer Space Telescope's Infrared Spectrograph

The heart of the Spitzer Space Telescope's instruments are its detectors. Spitzer will carry the best infrared astronomical detectors to date. The Multiband Imaging Photometer for Spitzer (MIPS), which will observe in the far-infrared, will detect objects 100 times fainter than have ever been seen before. One of the MIPS cameras, which will operate at 70 microns (a micron is one millionth of a meter), contains 1,024 detectors and is 100 times larger than previous arrays operating in space. Each detector has about 30 times the sensitivity of past detector arrays at this wavelength. Another MIPS camera, which is operated at 160 microns, has 10 times as many detectors, with 10 times the sensitivity, as any previous array operated in space at this wavelength. The Infrared Array Camera (IRAC) will produce near-infrared images using four 256 x 256 pixel detector arrays! Spitzer's Infrared Spectrograph (IRS) will perform spectroscopy in the mid-infrared using 128 x 128 detector arrays.