NIRCam
NIRCam is an instrument aboard the to-be-launched James Webb Space Telescope. It has two major tasks, as an imager from 0.6 to 5 micron light wavelength, and as a wavefront sensor to keep the 18-section mirrors functioning as one. In other words, it is a camera and is also used to provide information to align the 18 segments of the primary mirror. It is an infrared camera with ten mercury-cadmium-telluride (HgCdTe) detector arrays, and each array has an array of 2048 X 2048 pixels. The camera has a field of view of 2.2 X 2.2 arc min with an angular resolution of 0.07 arcsec at 2 microns. NIRcam is also equipped with coronagraphs, which helps to collect data on exoplanets near stars. It helps with imaging anything next to a much brighter object, because the coronagraph blocks that light. NIRcam is housed in the Integrated Science Instrument Module, to which it is attached physically by struts. It is designed to operate at 37 kelvin (roughly minus 400 degrees Fahrenheit), so it can detect infrared light at this wavelength. It is connected to the ISIM by struts and thermal straps connect to heat radiators, which helps maintain its temperature. The Focal Plane Electronics operated at 290 kelvin.
NIRcam should be able to observe as faint as magnitude +29 with a 10000-second exposure (about 2.8 hours). It makes these observations in light from 0.6 (600 nm) to 5 microns (5000 nm) wavelength. It can observe in two fields of view, and either side can do imaging, or from the capabilities of the wave-front sensing equipment, spectroscopy. The wavefront sensing is much finer than the thickness of an average human hair. It must perform at an accuracy of at least 93 nanometers and in testing it has even achieved between 32 and 52 nm. A human hair is thousands of nanometers across.
Wavefront sensors components include:
Parts of NIRCam:
NIRCam has two complete optical systems for redundancy. The two sides can operate at the same time, and view two separate patches of sky; the two sides are called side A and side B. The lenses used in the internal optics are triplet refractors. The lens materials are lithium fluoride (LiF), a barium fluoride (BaF2) and zinc selenide (ZnSe). The triplet lenses are collimating optics. The biggest lens as 90 mm of clear apature.
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