Grid-gated photomultiplier photometer with subnanosecond time response

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Abstract
A grid‐gated photomultiplier has been used in the construction of a subnanosecond‐time‐resolved photometer. The photocathode is gated on during a sampling window which occupies 4 ns of an 8‐ns mode‐locked ion laser cycle. The 0.5‐ns rise‐time sampling window is derived from the mode‐locker drive signal and can be adjusted in phase relative to the incident laser light pulses. By resolving scattered light pulses from long‐lived fluorescence, the photometer affords a 20‐fold reduction in scattered light interfering with photobleaching recovery measurements of low‐level fluorescence. Moreover, it has permitted the time‐domain measurement with dc circuitry of fluorescence lifetimes as short as 0.7 ns. This time response is achieved using a photomultiplier which, in the absence of grid gating, exhibits an anode pulse rise time of 18 ns. Additional applications of this device and of a related narrow‐window sampling photometer currently under development are discussed.
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