SPECS 2D-CCD, User Manual

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Manual V2.docx | Status 10.12.2015 | Version 1
6 Principles of the CCD Detector
The CCD detector has a set of micro-channel plates (MCPs) which can produce a 2D picture
of the electrons emerging from the analyzer. This allows you to view data in dispersive as
well as non-dispersive directions; for example, to obtain angle-resolved or spatially resolved
information.
This chapter contains a description of the MCPs and background information about the
cameras used to acquire images from the MCPs. Some data is also provided to show the
capabilities of a SPECS CCD detector.
Camera 6.1
The charge-coupled device (CCD) is a silicon light sensor which converts incident light, or
photons, into electrons. Analog-to-digital converters (ADCs) are employed as a measurement
of pixel value or brightness. These have 12 bit resolution, corresponding to 4095 gray levels,
or ADUs. The relationship between the ADUs generated and the number of electrons
acquired on the CCD is defined by the system gain.
Intensities given in ADUs provide a convenient method for comparing images and data
generated by different cameras. This is also referred to as count and digital number. Pixel
voltages (numbers of electrons) stored during CCD integrations are converted to ADU
integers representing the measured voltage compared to maximum (full pixel) voltages in
terms of the full dynamic range of the CCD system.
Linearity 6.2
The fundamental process that occurs in CCD imaging is the conversion of photonic input to
electronic output. The transfer function between the incident photonic signal and the final
digitized output should vary linearly with the amount of light incident on the CCD.
High-performance CCD sensors like those used for the SPECS CCD detector have extremely
good linearity. Deviations from linearity are often less than a few tenths of a percent for over
five orders of magnitude. This is far superior to video CCDs and other solid-state sensors
which can exhibit non-linearity of several percent or more. For quantitative imaging, linearity
is a strict requirement. CCDs must be linear in order to perform image analysis such as
arithmetic ratios, shading correction, flat fielding, linear transforms, etc.
Manual V2.docx | Status 10.12.2015 | Version 1