Specifications

Version 1.1 rev Jan 2013
Page 44
iXon Ultra
Features & Functionality
3.1.5 - EM Gain dependence and stability
EM Gain is a function of the EM voltage and of the sensor operating temperature. When the user applies gain
through the software, it is the EM voltage in the gain register that is varied. As can be seen from Figure 12 below, the
dependence of EM Gain on EM voltage is sharp (note the logarithmic scale). This arises because the signal electrons
acquire energy as they are accelerated through the EM electric eld, and once this eld strength reaches the threshold
needed to overcome the bandgap energy, the impact ionization rate rises rapidly. Historically, this sharp dependence
has meant that the software control of EM Gain in all EMCCD cameras has been via a non-linear scale with most of
the amplication occurring within a relatively small portion at the top of the overall scale. Thus considerable ne tuning
by the user to determine an optimal gain setting has been required, and even then the actual gain is determined only
through measurement of a stable light source, with and without gain applied.
Figure 12: EM Gain vs EM clock voltage
The effect of sensor temperature on EM Gain is shown in Figure 13. This dependence arises primarily from photon
scattering of electrons when they are accelerating in the EM electric eld. The scattering causes a loss of energy, which
increases with temperature. To make up this loss and maintain EM Gain, a larger EM electric eld must be used at higher
temperatures. As can be seen from Figure 13, EM Gains well in excess of x1000 can be achieved at low temperatures.
However, it is not recommended to use gains above x1000 because such high gains can cause signicant ageing of the
gain register (see EM Gain Ageing in Section 3.1.7).
Figure 13: EM Gain vs sensor cooling temperature