  Flux dependent non-linearity (reciprocity failure) in HgCdTe near infrared
detectors can severely impact an instrument's performance, in particular with
respect to precision photometric measurements. The cause of this effect is
presently not understood. To investigate reciprocity failure, a dedicated test
system was built. For flux levels between 1 and 50,000 photons/s, a sensitivity
to reciprocity failure of approximately 0.1%/decade was achieved. A wavelength
independent non-linearity due to reciprocity failure of about 0.35%/decade was
measured in a 1.7 micron HgCdTe detector.
