抄録
For the observation of light waves emitted by electroluminescent cells, the usual procedure employed is that the light is first received by a photomultiplier tube and amplified, then the wave form is thrown on a Braun tube screen. By this means, only the alternating component of light waves can be observed. Investigation of electroluminescence requires not only the alternating component but the height from zero level to the lowest value of the light waves to be determined. For this purpose, an apparatus for zero level indication on Braun tube oscillograph was devised. The principle of performance is that, during one cycle in every five cycles, potential of photocathode of the photomultiplier tube is raised higher than that of the first dynode suppressing the photoemission, and consequently the output of the photomultiplier tube is brought down to zero level. This apparatus is all-electronic and should be available for high frequency light waves. However, a double pulse decatron, used for counting cycles, limits the available frequency to a few kilocycles which is nevertheless considerably higher than with a mechanical light chopper.
