integral field spectrograph

An integral field spectrograph (or integral field spectrometer) combines spectrography and imaging, producing a data across three dimensions (e.g., a data cube), two being spatial (the image) and one being the spectral data at each specified point. Its use is called integral field spectroscopy (IFS).

An integral field spectrograph is commonly a normal spectrograph plus an integral field unit (IFU). A normal spectrograph only collects data from within a narrow line-like area (a slit) rather than from an area with two more-equal dimensions of the full focal plane, giving the spectrum one dimension to spread out on, but offering spectral data over basically just one spatial dimension, and a succession of observations would be needed to cover the other spatial dimension. The IFU rearranges portions of the image so that the spectrograph's narrow slit includes signal over a two-dimensional area, but trading away some angular resolution. IFU spectrographs are often designed so they can also operate without it, offering normal spectrography as well. IFU methods used:

• Image slicer uses a series of adjacent narrow, rectangular reflectors that each span one dimension of the focal plane, each covering a slice of the image, their reflection such as to arrange the image so the slices of it are aligned end-to-end within the spectrograph's slit. I think a collimator at a focal plane is necessary. UVES of the ESO VLT does this.
• Lenslet array has a lens for each pixel. SAURON of the William Herschel Telescope (WHT) uses this.
• Fibers uses optical fibers to direct the image into a single slit. INTEGRAL, used on the WHT uses this.