KOALA, the Kilofibre Optical AAT Lenslet Array, is a wide-field, high efficiency, integral-field unit designed for use with the bench mounted AAOmega spectrograph on the AAT. KOALA has 1000 hexagonal lenslets in a rectangular array. The field of view is selectable between either 15.3 x 28.3 arcsec (0.7" sampling) or 27.4 x 50.6 arcsec (1.25" sampling). To achieve this, KOALA uses a telecentric double lenslet array fed by interchangeable fore-optics. The IFU is mounted at the f/8 Cassegrain focus and feeds AAOmega via a 31m fibre run.
KOALA benefits from all of the flexibility of the reconfigurable AAOmega spectrograph. The double beam spectrograph provides user selectable wavelength coverage and resolution using a series of movable, interchangeable gratings. A set of low, medium, and high resolution gratings provide R ~ 1,000, R ~ 5,000 or R ~ 10,000 across the wavelength range 330 nm to 900 nm. Each arm can be independently configured. The two arms are separated by a dichroic mirror with either a 570nm or 670nm cut. Full spectral coverage is possible in a single exposure with the low-resolution gratings.