Performance Summary

From the field of 20 detectors, the best 16 detectors are selected for the IR camera focal plane leaving 3 potential spares and a true engineering detector. Figure 6 shows the bitmaps of these 16 detectors through K-band. The numbers identify the each module by its serial number. These bitmaps are stretched between the same limits, so it is apparent that a couple of earlier modules (22 and 23) have relatively low QE around 70%. Most of the detectors showed high QE over 90% and some showed near and above unity (100% QE). Modules 22 and 23 have unstable, hygroscopic Anti-Reflection (AR) coatings and are needed to be stored in a dry environment. All modules from #25 onwards have received robust AR coating and also exhibit high QE. The other features in these bitmaps are the large area cluster defects on module#35 (up to 1.8% pixels), excess hot pixels on modules#30 and #43 and a column defect on #43. Most of the detectors achieved pixel operability over 98% with few exceeding 99% operability and met specifications with sufficient margin. Modules#30 and #43 possess excess hot pixels but the mean dark generation is well within the specifications. Cosmetically, the distinguished feature of these detectors is the numerous defective spots across the array, but some detectors have not shown such spots. Cluster defects ~20 pixels in diameter are present in most of the detectors. The read noise is ~17e- in most of the detectors and could be reduced under 6e- with multiple sampling. Table 1 summarises the performance of the module SCA-45. More performance data on these detectors is also presented by Love, et al. [3].

Figure 6. K-band bitmaps of the 16 VIRGO detectors (the numbers identify the modules by the manufacturers serial numbers).

Some of the detectors showed cosmic events throughout the tests. The events are quire irregular: some are tiny blobs, some spread over tens of pixels and few are like comet tails. As these events are not seen in few other detectors, the source of these events is unknown.

Table 1. Performance summary for SCA-45.


SCA-45 (72K)


Quantum Efficiency

92% (J), 101%(H), 95%(K)

Radiometry uncertainty ~12%

Well capacity


Measured at 0.7V bias

Dark Generation


From operable pixels


15.4e- (rms)

Temporal noise method



From 10 - 80% full well

Persistence signal


in a 10s dark after 1min

Pixel Operability


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