horiba JOBIN YVON SYNAPSE, Руководство пользователя

Страница: 107 / 116

Glossary of Terms
97
residual charge always remains present on the CCD output node even after the CCD’s
reset gate has been activated once a pixel has been read out. Thus, this process
ensures that only the true charge associated with the current pixel being processed is
measured.
Cosmic Ray Events
Cosmic Rays are high-energy particles from space, mostly attributed from the sun.
They will generally be detected by a scientific grade detection system, since the
cooled CCD offers extremely low dark signal level. In the active area of a typical
array, about 5 events per minute per sensor cm
2
may occur. Compared to very weak
signals from the experiment at hand, detected comic ray events can be quite
distracting. To minimize the effects of these rays, the end-user can utilize the smallest
section of the chip required by the experiment, as well as, use the smallest integration
time possible. In addition, mathematical treatment of the data can also be used to
remove these spurious spikes in the spectra. Please refer to the SynerJY software
manual for more information about cosmic removal.
Dark Signal
Dark signal is generated by thermal agitation. This signal is directly related to
exposure time and increases with temperature. The dark signal doubles with
approximately every 7
o
C increase in chip temperature. The more the dark signal, the
less dynamic range will be available for experimental signal. This signal accumulates
for the entire time between readouts or flushes, regardless of whether the shutter is
open or closed. Dark signal is also generated during the charge transfer cycles of the
CCD. The problem is not necessarily the dark signal, but the noise in measuring the
signal that adversely affects the data.
Dark Signal Nonuniformity (DSNU)
Dark signal nonuniformity (DSNU) is the peak-to-peak difference between the dark
signal generation of the pixels on a CCD detector in a dark exposure.
Dynamic Range
Dynamic Range is the ratio of the maximum and minimum signal measurable. For a
16-bit detection system, the ideal / optimum dynamic range would be represented by
65,535:1. With respect to a CCD, this performance figure of merit corresponds to the
ratio of a pixel’s full well saturation charge to the output amplifier’s read noise. It
should be noted that the pixel’s full well saturation charge correlates directly to the
CCD’s well capacity and varies with the device’s pixel size and overall structure.
A more useful calculation of dynamic range, so far as a CCD sensor is concerned,
centers around the “effective system” dynamic range. This system level parameter
corresponds to the ratio of a CCD pixel’s “linear” full well saturation charge to the
total system noise level.
Effective System Dynamic Range = Pixel Linear Full Well Saturation Charge
Total System Noise