SB375 @ 1 sec. Scan Time (part 1)

Dzung and Bob ran a series of tests with an SB375 array to see how well it works at 1s scan times. If it works well, operation at the IRTF will be more like TEXES in terms of observing schemes.

The data have been moved to the 'SaltLick' server in the EXES lab. You can find it in /Reduced/SB375_Det_Lab/EXESSB375_SCA_128_100915. There are four subfolders:

- DKI_BB7K_7K_varyVdet_varyFD_1

- DKI_BB7K_7K_varyVdet_varyFD_2

- PhotoI_BB45K_7K_varyVdet_varyFD_1

- PhotoI_BB45K_7K_varyVdet_varyFD_2

The folders ending in '1' are taken at 1s scan time, the others at ~2.7s scan time. Within each folder are a series of frames taken at different integration times and different detector biases. What I'd like to know first is whether the detector response is comparable at the two scan times.

Ran the data through the 'aida_getstats' IDL routine to gather summary statistics, plotted here:

This is a messy plot. The data show mean-pixel signal for different integration times and biases. Each series shows discontinuous segments, each of which corresponds to a different detector bias. At a given bias, there are 11 measurements at frame delay values times incremented by 1s from one point to the next, over a range of zero to ten seconds. The 2.7s (blue) data took longer to collect due to increased scan time. The data plotted are all fowler-4 results.

Ideally these segments should all be straight lines, since the detector response should be linear at a given bias and the integration time is changing linearly. The fact that the segments are not straight shows that the detector response is non-linear. The 2.7s (blue) data beyond about 7.5ks (and the 1s data beyond 5ks) elapsed time are essentially flatlined, because the

detector is saturated. The very early data is curved because low detector bias levels lead to early debiasing effects. Basically, most of this data set is not useful.

But let's look at the third segment in each set, which is not railed, and not at zero bias. For these segments, the applied bias is -1V, and while we see some curvature, we don't hit a hard rail anywhere.

Units are arbitrary, and there is an offset between the two curves, but the signal is actually a little higher for the 1s-scan time based on slope. This may be due to a slightly higher effective bias at each integration time due to the faster scan time (less debiasing), but it would be nice to see some data collected with less photon flux in the detector FOV so that more of the data could be analyzed. Dzung is taking another cut at this experiment this week.

More work to do, but this set of data is encouraging. I was concerned that the array would not respond at this speed, or that it would fail to reset, etc. So far, so good.