Princeton Instruments ProEM+ EMCCD, Руководство пользователя

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64 ProEM
®
+ System Manual Version 1.B
9. Wait until the calibration has been completed (it might take 10 minutes or
longer), and then close the dialog before starting the application program. If the
camera is a
ProEM+:1600 , the process may take 30 minutes or longer .
CCD Temperature
As stated before, lowering the temperature of the CCD will generally enhance the quality
of the acquired signal by lowering dark noise. In EMCCD cameras, lower temperatures
will also result in higher EM gain. When WinX is the controlling software, temperature
control is done via
Setup | Detector Temperature. When Light Field is being used,
temperature control is done on the Sensor expander. Initially, the default temperature
appropriate for your specific model is displayed.
Once the target array temperature {Temperature Setpoint} has been set, the software
controls the camera's cooling circuits to reach set array temperature. On reaching that
temperature, the control loop locks to that temperature for stable and reproducible
performance. When temperature lock has been reached (temperature within 0.05°C of set
value) the current temperature is
Locked . The on-screen indication allows easy
verification of temperature lock.
The time required to achieve lock can vary over a considerable range, depending on such
factors as the camera type, CCD array type, ambient temperature, etc. Once lock occurs, it is
okay to begin focusing. However, you should wait an additional twenty minutes before taking
quantitative data so that the system has time to achieve optimum thermal stability.
When vibration may affect results, you can turn off the fan operation while making sure
that the coolant is circulating through the camera to maintain the CCD cooling
temperature. If the fan is turned off and there is no coolant circulating through the
camera, the built-in thermo-protection switch may shut the camera down to prevent
thermal damage. In the event that this occurs, wait about ten minutes, correct the situation
that caused the shutdown, and re-power the camera.
The deepest operating temperature for a system depends on the CCD array size and
packaging. Refer to Table 5 (page 122), for default cooling temperatures.
Note:
If the CCD is cooled to low temperatures (below -50°C), exposure to ambient
light will over-saturate it. This may increase dark charge significantly. If the camera
remains saturated after all light sources are removed, you may have to bring the camera
back to room temperature to restore dark charge to its original level.
Dark Charge
Dark charge (or dark current) is the thermally induced buildup of charge in the CCD over
time. The statistical noise associated with this charge is known as dark noise. Dark charge
values vary widely from one CCD array to another and are temperature dependent.
With the light into the camera completely blocked, the CCD pixels accumulate thermally
generated electrons, dependent on the exposure time and camera temperature. The longer
the exposure time and the warmer the camera, the less uniform this background will
appear. Thus, to minimize dark-charge effects, you should operate at the default CCD
temperature.
Bias Active Stabilization Engine
(BASE™)
All CCDs and EMCCDs produce a baseline output signal even when there is no incident
light and the exposure is zero. Camera electronics process this information to produce
what is known as a bias image. For quantitative applications, it is critical that the bias