Measurements of He I Lifetimes and Fine Structure by a Two-Spectrometer Method
We have developed a two-spectrometer procedure which gives an accurate time scale in beam-foil experiments. The foil-excited beam is simultaneously viewed by two optical spectrometers. In He I studies one of these spectrometers observes the 3889 Å line (1s2s 3S − 1s3p 3P) where the accurately known 3P2 − 3P1 separation of 658.55 MHz serves as the calibration frequency. The other spectrometer can be set to any He line. By this technique we have studied the lifetimes of the 1s3p1p levels and the fine structure for 1s4p 3P and 1snd 3D (n = 3−6).
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