drive a periodic waveform and sample repeatedly. Assuming you don't somehow sample the same point in the periodic waveform each time, you'll eventually get the complete waveform.
> Assuming you don't somehow sample the same point in the periodic waveform each time, you'll eventually get the complete waveform.
To add an example of a real technique: You can use a short laser pulse and change the time-of-flight (mirrored path on a stepper motor, for instance). This technique will get you to the terahertz region, which is pretty much state of the art for where electronic devices still have gain.
