time-interval measurement

time-interval measurement [′tīm ‚in·tər·vəl ‚mezh·ər·mənt]

(horology)

A process that consists either in calculating the duration between two known epochs, or in counting the repetitions of a recurring phenomenon from an arbitrary starting point, as with an electronic digital-reading counter, which counts the cycles of an oscillator.

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Time-interval measurement

A determination of the duration between two instants of time (epochs). Time intervals are measured with high precision with a digital display counter. An electronic oscillator generates pulses; the count begins with a start signal and ends with a second signal. Two atomic clocks can be compared in epoch to 1 picosecond (1 ps = 10^-12 s) by electronic interpolation. See Atomic clock, Oscilloscope

Rapid motions can be studied at short intervals by means of a large variety of high-speed cameras, including stroboscopic, rotating film-drum, rotating mirror, streak, and image converter cameras. An electronic streak camera can separate two pulses 1 ps apart.

Ultrashort laser pulses are used to study rapid processes caused by the interaction of photons with an atom or molecule. Pulses as short as three wavelengths of 620-nm light, with &tgr; = 6 femtoseconds (1 fs = 10^-15 s), have been formed. See Laser, Optical pulses

Radioactive decay is used to measure long time intervals, to about 5 × 10⁹ years, concerning human history, the Earth, and the solar system.