Output Noise Characteristics of Vacuum Photodiode Circuits

The effect of the biasing circuit configuration on the output noise spectra of the vacuum photodiode was investigated. It was found that under certain biasing circuit conditions, the output noise spectra were frequency dependent, resembling the 1/f noise spectrum at moderate frequencies. This similarity and its cause should be noted to avoid possible misinterpretation of data or erroneous measurements. Also, the conditions for obtaining white output noise spectra (and thus flat frequency-response curves) are presented. The measured white noise levels were found to be slightly in excess of that predicted by shot noise considerations alone.