Recording fast transient phenomena with cathode ray oscillograph in free air as well as in high vacuum

In spite of the great improvements which the cathode-ray oscillograph for high-vacuum photography has undergone in the last few years, the problem of photography in free air is most important on account of the great simplifications for general construction and for taking of photographs. An available method for taking photographs outside the vacuum, was found to be the employment of an electron permeable window (Lenard window) of the size of the oscillogram to be made. Ordinary aluminum or cellon foil of approximately 7 or 16 μ, thickness respectively may be used if the common exciting voltages of 66–75 kv. are employed. With such foils, all results are to obtain which hitherto have been feasible only with high-vacuum photography. According to this method, oscillograms in free air were taken which attained recording speeds up to 5000 km. per sec, using an exciting voltage of 75 kv. only. With this recording speed, details in the oscillograms of the duration of one milliardth of a second may be dissolved. As compared with the high-vacuum photography hitherto exclusively used for recording quickest phenomena, the Lenard window oscillograph allows taking photographs in a considerably shorter time with the advantages of the simpler construction and manipulation.