Recent experimental results on developmental pulse amplifiers are described. Risetimes of 1 nanosecond with pulse output powers greater than 1 kW have been obtained. Current pulses in excess of 100 amps with risetimes of less than 5 ns into a half ohm load have also been realized. The high-current pulse amplifier has produced peak powers in excess of 8 kW. A comparison of theoretical and experimental results is given based on the large-signal computer simulation of EBS amplifier perform- ance. Recent technological improvements in semiconductor target fabri- cation, electron-beam formation, and EBS device processing are described. Life test data on the two types of pulse amplifiers showing stable target characteristics under beam bombardment is presented.

6.3 HIGH SPEED 0.63 MICRON HYBRID PHOTOMULTIPLIER TUBE, T. Yasar and C. E. Catchpole, Bendix Research Labora- tories, Southfield, Michigan and J. R. Sizelove, Air Force Avionics Laboratory, Wright-Patterson AFB, Ohio

This paper describes the development and performance of an electron beam-semiconductor hybrid photomultiplier tube for gigahertz laser com- munications.

The photomultiplier tube consists of a photocathode, with peak sen- sitivity at 0.53 pm corresponding to light from a Nd-YAG frequency doubled laser source, and a fast silicon diode in parallel proximity to the photocathode. The diode is mounted on a specially designed 50 ohm co- axial feedthrough at the base of the tube. The low-noise property of the detector is preserved by transferring the processed photocathode through the vacuum system into its final position in the tube. This technique is also necessary to prevent degradation of the diode characteristics during processing. The reverse biased silicon diode acts as the electron multiplier and collector. The bandwidth and S!N considerations for this hybrid photomultiplier tube will be presented. The solutions of the problems associated with the compatibility of the tube components with each other and with the tube processing techniques will be given.

The devices are required to have a gain of lo8 and subnanosecond response time. The finished tubes, with photocathode response peak a t 0.53 p m show an output pulse width (at 10% points) of 0.7 nanoseconds and an electron gain of los. The pulse rise time is less than 0.2 nanoseconds and jitter is less than 0.1 nanoseconds.

This work was partly supported by the Air Force Avionics Laboratory, WPAFB, Ohio under contract No. F33615-71-C-1851.

6.4 FAST FIVE-STAGE PHOTOMULTIPLIER WITH GaP(Cs) DYNODES, D. E. Persyk and D. D. Crawshaw, RCA, Lancaster, Pennsylvania

The use of negative-electron-affinity materials as secondary emitters results in marked performance improvements in photomultiplier detectors. This paper treats the developmental type C31024 photomultiplier which utilizes five GaP(Cs) dynodes to provide gains of the order of 5 X 106. The high secondary emission ratio (greater than 20) of the GaP(Cs) dynodes permits the electron-multiplier section of the device to resolve photoelectron inputs consisting of 1, 2, 3 or 4 electrons as discrete events. The single-electron anode pulse rise time is 800 p ~ . Data are presented on time- and frequency- domain measurements and a comparison of meas- urement techniques is presented. Applications are discussed in the fields of laser-light detection and medical electronics.

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