Figure 24. Setting The Avalanche Gain (Experiment Setup|Main Tab Page) - Princeton Instruments PhotonMAX System Manual

Chapter 5 Operation 41
Avalanche Gain (Multiplication Gain)
As explained previously, the PhotonMAX uses a
unique CCD capable of multiplying the charge
(electrons) generated in the pixels. When the
multiplication is sufficiently high, it is possible
to see extremely low-light events. The amount
of multiplication is controlled by the voltage
applied to multiplication register clocks. For
convenience, a 12-bit DAC (digital-to-analog
converter) is provided to adjust the
multiplication factor in 4096 steps. The digital
value is proportional to the clock voltages,
which in turn has a complex relationship
(approximated to an exponential) with the level
of multiplication.
When the Multiplication Gain port is selected
( Experiment Setup|ADC tab page), the
Avalanche Gain can be set by entering a digital
(DAC) value on the Experiment Setup|Main
tab page. A Gain setting of zero (0) refers to a
no-gain state where the camera behaves like a
standard high speed CCD (with rather high read
noise). Values 1 to 4095 are mapped linearly to
the internal serial clock voltages that vary the
Figure 24. Setting the Avalanche Gain
multiplication gain in a complex exponential
(Experiment Setup|Main tab page)
fashion. Typically at a Gain setting of 4095, the
PhotonMAX can offer a multiplication gain factor in the excess of 1000x. Even though the
camera is capable of delivering large multiplication gain factors, multiplication gain should
be used only as needed to preserve as much dynamic range as possible.
The avalanche gain for your camera is measured at various Gain (DAC) settings and the
data are provided on the Certificate of Performance. A typical relationship between the
DAC setting and charge multiplication factor for the PhotonMAX:512B is shown in the
graph below.
Figure 25. DAC Setting vs. Charge Multiplication Gain