The FGS PMTs (four per FGS) are end-illuminated, 13 stage venetian blind dynode S-20 photon-counting detectors with an effective photocathode area of about 4 mm. The A and B channels for each FGS interferometric axis operate independently. The PMTs are sensitive over a bandpass of 4000-7000A, with an efficiency of ~ 18% at the blue and diminishing linearly to about 2% at the red end.
The FGS1r dark counts for each channel are given in Table 2.1:.
PMT |
counts/second1 |
stdev |
---|---|---|
AX |
174.6 |
±2 |
BX |
84.4 |
±2 |
AY |
164.0 |
±2 |
BY |
252.0 |
±2 |
1Values based on an average of 40Hz PMT counts and associated standard deviations. |
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |