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Chapter 8
Correction Techniques
Introduction
Advanced data collection includes background subtraction, flatfield correction, CCD
blemishes removal and Cosmic Ray removal. The skillful use of these techniques can
significantly enhance measurement capabilities. Note that not all correction techniques
will be available in early releases of the software.
Background Subtraction
Princeton Instruments systems are adjusted so that data have a small offset. This offset
assures that small signals won’t be missed. This offset can be subtracted after the signal
is acquired to prevent it from having any influence on the data.
Background subtraction allows you to automatically subtract any constant background in
your signal. This includes both constant offsets caused by the amplifier system in the
controller as well as time-dependent (but constant for a fixed integration time) buildup of
dark charge. Some users collect background spectra with the shutter open, including
ambient light in their background data. The background subtract equation is:
(Raw image data – Background) = Corrected image data.
When background and flatfield operations are both performed, background subtraction is
always performed first. The equation is the following:
(Raw image data – Background)/Flatfield = Corrected image data.
Below are instructions for collecting and using background data files.
Acquiring background files
This operation is similar to normal data acquisition.
➧ Use exactly the same temperature setting as will be used in data collection. Wait at
least 30 minutes after the detector has reached operating temperature to ensure
stability.
➧ Set the same binning parameters, ROI and Exposure.
➧ Select
Acquire Background
from the Acquisition menu. This will immediately
acquire a background file using the Experiment Setup parameters, only the shutter
will remain closed for most applications.
To acquire a background with the shutter open, or if the Acquire Background feature is
too restrictive in some other way, a background file can be collected as a normal data