You need to provide a series of voltages to the dynodes of a photomultiplier to make it work.

A resistive voltage divider will give good performance provided the mean anode current is less than 1% of the divider current.

Figure 1 shows a resistive voltage divider, known as a uniform divider, each interdynode resistor is of the same value.

In the tapered version, figure 2, resistor values increase towards the anode. This is to overcome space charge effects which lead to non-linearity when dealing with high current pulses. For optimum performance, V(k-d1) is often higher than the interdynode voltages and hence R(k-d1) ranges over 2R, 3R....., 8R, depending upon pmt type.

In a variant of the all-resistor divider, figure 3, a zener diode replaces the resistor between k and d1. This maintains V(k-d1) constant regardless of the high voltage setting and ensures good collection and fast response when the photomultiplier is operated over a wide range of gain settings.

For pulsed light applications, decoupling capacitors need to be connected across the last three or four dynodes to provide transient signal charge. These may be omitted in dc applications but are normally included in ET Enterprises' voltage dividers.

The standard inter-dynode resistor value is 330 kΩ but other values can be supplied to special order. All voltage divider types can be supplied with high voltage and signal leads, with or without connectors, to your specification.

Further information on voltage dividers can be found in our photomultiplier brochure, technical reprint Photomultiplier Voltage Dividers RP/085, which can be obtained by contacting us.

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