Abstract

Sampling techniques are frequently used in order to measure the shape of repetitive pulses. They imply a synchronous trigger plus a variable delay and a peak sensing device which often sets the limit to the time resolution thus achievable. The best sampling oscilloscopes have a rise time in the range of 10 ps but they cannot be used for single shot measurement. A streak camera with a display of the pulse on a memory tube makes it possible to reach a resolution of 1 ps. However, the use of a streak camera is cumbersome and cannot be done on line because of the time needed for digital image evaluation. In some cases, transient recorders may be used, but the passband of such apparatuses is at present only of 6 GHz, which is insufficient for studying very brief light pulses. An alternative procedure consists in measuring the times of occurrence of events whose probability is proportional to the pulse height. The histogramme of these occurrences reproduces the pulse shape, provided the event probability is small enough for multiple event rate to be negligible. This method, called here stochastic sampling, is attractive because it consists in measuring the time of flight between a detected photon and a base time clock; and time measurements can easily be performed with TDCs or TACs to a resolution better than 10 ps. It is proposed to store the light pulse in a system of optical fibres which will deliver single photons as a periodic function. This will speed up the sampling by orders of magnitude, and eventually allow for single shot measurements.

© 1992 The Author(s)