External PMT amplifier
We have used a high-speed op-amp (LT1355, Linear
Technology, http://www.linear.com/) to
construct the amplifier for the external PMT.
A simple-minded non-inverting DC amplifier (see figure below) circuit was
built with two resistors (R1=1.0kW
Two serially connected 9Vbatteries were used as the power supply to the
op-amp, to avoid 60Hz main noise. Being
a very fast nano-second event, the pulse signal generated by a single photon
event was amplified by approximately 5 fold.
Some negative deflection was seen in the amplified signal in the
end-phase of the pulse signal, however, it was relatively smaller in amplitude.
Since the amplified pulse signal is integrated by the confocal controller
to compute the intensity of a pixel we anticipate that the effect of the
negative deflection is negligible.