OPERATING CIRCUIT AND CONTROL METHOD FOR A PHOTOMULTIPLIER
A operating circuit and control method for protecting a PMT having a photocathode, a plurality of dynodes and an anode against overloading with a shorter reaction time, and to allow it to be switched on again rapidly. For this purpose, a switch is provided for electrically short circuiting the photocathode with the first dynode, or a switch is provided for reversing the polarity of the voltage between the photocathode and the first dynode.
1 . An operating circuit for a photomultiplier which has a photocathode, a plurality of dynodes and an anode, the operating circuit comprising:
an electrical circuit to apply to the dynodes a respective voltage with respect to the photocathode; and
a switch, the switch being connected to the photodiode and the dynode that is closest to the photodiode for electrically short circuiting the photocathode with the closest dynode.
2 . The operating circuit according to claim 1 , further comprising:
a first comparator connected to the switch for comparing an anode signal from the anode with a predetermined first threshold value, wherein the anode signal closes the switch, if a value of the anode signal exceeds the first threshold value.
3 . The operating circuit according to claim 2 , further comprising a second comparator for comparing the anode signal with a predetermined second threshold value, where the second comparator is connected to the switch, and opens the switch, if a value of the anode signal falls below the second threshold value.
4 . The operating circuit according to claim 3 , where the two comparators are identical.
5 . The operating circuit according to claim 3 , where the two threshold values are identical.
6 . A light scanning microscope comprising:
a photomultiplier having a photocathode, a plurality of dynodes and an anode,
an electrical circuit to apply to the dynodes a respective voltage with respect to the photocathode; and
a switch, the switch being connected to the photodiode and the dynode that is closest to the photodiode for the electrical short circuiting of the photocathode with the closest dynode.
7 . The light scanning microscope according to claim 6 , where the electrical switch comprises a switch with a maximum reaction time of 1 μs.
8 . A control method for a photomultiplier having a photocathode, a plurality of dynodes and an anode, comprising the steps of stressing the dynodes by a respective voltage with respect to the photocathode, and short circuiting the photocathode with the dynode that is closest to the photocathode.
9 . The control method according to claim 8 , wherein the short circuiting occurs, if it is identified that a value of an anode signal from the anode exceeds a predetermined first threshold value, where the short circuit is interrupted, if it is identified that a value of the anode signal from the anode falls below a predetermined second threshold value.
10 . The operating circuit according to claim 1 , wherein the remaining dynodes, in the case of a short circuit of the first dynode with the photocathode, present an electrical potential with respect to the photocathode, which is not zero.
11 . An operating circuit for a photomultiplier having a photocathode, a plurality of dynodes and an anode, the operating circuit comprising:
an electrical circuit for the application to the dynodes of a respective voltage with respect to the photocathode; and
an electrical circuit for reversing the polarity of a voltage between the dynode that is closest to the photocathode, and a photocathode and
a control unit which activates the polarity reversal, if the control unit identifies that a value of an anode signal from the anode exceeds a predetermined first threshold value, and deactivates the polarity reversal after a predetermined time period.