The ET Enterprises' range of fast photomultipliers has a focus electrode that can be biased negative with respect to the photocathode to cut off the photoelectron input to the multiplier section.
This is essential to avoid saturation of the photomultiplier output and processing electronics in applications such as fluorescence lifetime measurements and LIDAR.
Photomultiplier types with focus electrodes.
| 9214 | 9372 | 9426 | 9427 | 9813 | 9814 |
| 9817 | 9821 | 9822 | 9823 | 9921 | 9939 |
| 9954 |
Circuits
Two complimentary versions are available to gate ON or gate OFF a photomultiplier normally in the opposite state:
- GB1A switches OFF a normally ON photomultiplier
- GB1A/DC can be switched OFF indefinitely
- GB1A switches ON a normally OFF photomultiplier
Gating parameters, referred to in the table below, are defined in the diagrams below.
| GB1A | GB1A/DC | GB1B | |
| pmt voltage (max) | 2500V | 2500V | 2500V |
| gate level amplitude (max) |
5V, 50 mA | 5V, 50 mA | 5V, 50 mA |
| gate pulse width Gw (min) |
2 µs | n/a1) | 2 µs |
| gate delay d1 | 0.5 µs | n/a1) | 0.5 µs |
| gate delay d2 | 0.7 to 7 µs2) | n/a1) | 0.7 to 7 µs2) |
| gated pmt output width Ga (min) |
5 µs | 1 ms | 5 µs |
| gated output width (max) |
1 ms | 1 ms | |
| period (min) | 1000 x Gw | n/a | 1000 x Gw |
| t off | 0.2 µs | n/a1) | 0.2 µs |
| t on | 1.0 µs | n/a1) | 1.0 µs |
| cut-off ratio (typ) | 1000:1 | 1000:1 | 1000:1 |
Diagrams
1) DC gating board is not recommended for use in pulsed mode. The 5 V gate input should be switched manually, or from computer control.
2) Gating boards are powered from the voltage divider; the voltage divider resistances determine the recharging time. Generally, higher current dividers have shorter gate delay d2.
