  The central institute of electronics (ZEA-2) in the Forschungszentrum Juelich
(FZJ) has developed a system to scan the response of the photocathode of
photomultiplier tubes (PMT). The PMT sits tight on a supporting structure,
while a blue light emitting diode is moved along its surface by two stepper
motors, spanning both the x and y coordinates. All the system is located in a
light-tight box made by wood. A graphical software was developed in-situ to
perform the scan operations under different configurations (e.g., the step size
of the scan and the number of measurements per point). During each point
measurement the current output generated in the vacuum photomultiplier is
processed in sequence by a pre-amplifier (mainly to convert the current signal
into a voltage signal), an amplifier, and by an ADC module (typically a CAEN
N957). The information of the measurement is saved in files at the end of the
scan. Recently, software based on the CERN ROOT and on the Qt libraries was
developed to help the user analyzing deeper the data obtained by the scan. The
new software, cross-platform due to its build performed inside the Qt-IDE, is
described in this note.
