  Mid-infrared (IR) array detectors have been used for astronomical
observations in space. However, the uniformities of their spectral response
curves have not been investigated in detail, the understanding of which is
important for spectroscopic observations using large array formats. We
characterize the spectral responses of all the pixels in IR array detectors
using a Fourier transform infrared spectrometer and cryogenic optics for
measurements at high signal-to-noise ratios. We measured the spectral responses
of the Si:As impurity band conduction (IBC) array, a flight back-up detector
for AKARI/IRC. As a result, we find that the Si:As array has intrinsic
variations in the spectral response along the row and column directions of the
array. We also find that the cutoff wavelength of the Si:As IBC array depends
on the intensity of the incident light.
