![]() ![]() They are similar in principle to the detectors that convert visible light in a digital camera. The more pixels that can be placed on a detector of a given size, the greater the resolution, and NASA's QWIP arrays are a significant advance over earlier 300,000-pixel QWIP arrays, previously the largest available. NASA's QWIP detector is a Gallium Arsenide (GaAs) semiconductor chip with over 100 layers of detector material on top. Each layer is extremely thin, ranging from 10 to 700 atoms thick, and the layers are designed to act as quantum wells. Quantum wells employ the bizarre physics of the microscopic world, called quantum mechanics, to trap electrons, the fundamental particles that carry electric current, so that only light with a specific energy can release them. ![]() If light with the correct energy hits one of the quantum wells in the array, the freed electron flows through a separate chip above the array, called the silicon readout, where it is recorded. A computer uses this information to create an image of the infrared source. Image left: Another false color image with the QWIP camera of engineers and a seeing-eye dog (named Denver). This image illustrates the slight difference in temperatures of the scene – dark red being coldest and orange the warmest. Note the hand visible inside the labcoat pocket and the very warm tongue of Denver, curled in a yawn. Credit: NASA Print-resolution image (200 K jpg image) Also note the different hand temperatures of the people, some warm some cold. NASA's original QWIP array could detect infrared light with a wavelength between 8.4 and 9.0 micrometers. The new version can see infrared between 8 to 12 micrometers. The advance was possible because quantum wells can be designed to detect light with different energy levels by varying the composition and thickness of the detector material layers. "The broad response of this array, particularly in the far infrared - 8 to12 micrometers - is crucial for infrared spectroscopy," said Jhabvala.
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