Quantum Efficiency

Quantum Efficiencies (QE) are measured in J, H and K pass bands using blackbody radiometry. The uncertainties in QE measurements are up to 12% and are mainly due to the uncertainties in the blackbody temperature, emmissivity of the emitting surface, filter pass-bands and the estimation of conversion gain. The systematic error due to inter-pixel capacitance is being investigated. Another uncertainty that is difficult to estimate is the internal reflections within the test cryostat. Fig. 3 shows a QE histogram in K band from SCA-45 and a QE bar chart for all the 16 science detectors. QE in Z and Y bands has been measured on SCA-46 and the values are 70.7% and 81.0% respectively.

Quantum Efficiency

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Figure 3. (left) QE histogram for SCA-45 through K-band and (right) QE bar chart for all modules in J, H and K bands.

Performance Overview of the VISTA IR Detectors 3.3 Dark Generation

The dark generation is measured from a set of 240s CDS frames and it includes the reset transient. The detector shows slightly higher rate of dark generation immediately after the reset and reduces exponentially to its final value. The good pixels show negligible transient whilst the hot pixels show a large transient following the reset. As the test setup is not optimized for measuring low dark generation, it is possible that the reset transient is dominated by the background signal for good pixels. Figure 4 shows the dark histogram for SCA-45 and dark performance for the other detectors.

Dark Histogram


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Dark Generation

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22 23 25 30 31 33 35 36 38 39 41 42 43 44 45 46 Module#

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Figure 4. (left) Dark generation histogram from SCA-45 and (right) Dark generation for all the 16 detectors.

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