Abstract
We report here measurements of 1/f noise in vacuum photodiodes. The theoretical expression for the Hooge parameter αH is formally equivalent to the one for secondary emission 1/f noise. There is also 1/fγ noise due to fluctuations in the cathode work function; here γ∼3/2 is expected. The spectrum SIa( f ) for the latter varies as I2aV0a and for the former it varies as IaV3/2a, where Va is the anode voltage, and Ia the anode current. Enhanced shot noise was observed at higher frequencies; at lower frequencies the noise spectrum was of the 1/f type. The latter could be separated into a V0a component and a V3/2a component by measuring SIa( f ) vs Va. The V3/2a component of the 1/f spectrum could also be deduced from the current dependence of SIa( f ); both measurements mutually agreed well. The measured V3/2a component also agreed well with Handel’s predictions; by proper choice of the anode-cathode distance dca (dca=0.6 cm) almost exact agreement could be obtained. In view of the fact that the overall accuracy of the data is not better than 25%–30%, any value of dca between 0.4 cm<dca<0.8 cm should be considered as giving good agreement; this is a very plausible range of values. We observed some poisoning effects in older devices. They are attributed to the decomposition of the dynode material under electron bombardment and give rise to long-term instability of the device noise.
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