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70 NIRvana
™
-LN System Manual Issue 4
All NIRvana-LN arrays have been tested for uniformity and do not exhibit any vignetting
(i.e., reduction of response,) at the extreme ends of the array. If a reduction in response is
measured across the array, it may be the result of one or more of the following conditions:
•
Water condensation has occurred on the edges of the Dewar window. This will
occur only when the previously described cooling/pumping instructions have not
been followed or if the Dewar itself has sprung a leak. This is a very rare
occurrence.
•
The spectrograph is not illuminating the full photoactive area of the array. Most
spectrographs provide a minimum 1-inch-wide focal plane that should span the
entire array. If the exit port has been masked, the full focal plane may not be
available.
7.12 Software Binning
Binning is the process of summing data from adjacent pixels to form a single pixel that is
often called a Super Pixel. Because InGaAs arrays do not have a serial register or a
summing node, binning is accomplished in software after data have been read out and
digitized.
Software binning can be configured to occur automatically from the
Acquisition —>
Experiment Setup —> ROI Setup
tab {
Region of Interest
expander}.
The advantage of software binning is that it can improve the S/N ratio by as much as the
square root of the number of scans. Unfortunately, with a large number of scans (i.e., greater
than 100,) detector 1/f noise may reduce the actual S/N ratio to slightly below this
theoretical value. Also, if the light source used is photon-flicker limited rather than photon
shot-noise limited, this theoretical signal improvement cannot be fully achieved. Again,
background subtraction from the data is necessary.