Autocorrelator
Autocorrelator turns up in 2 fields: photonics, electronics. Here is what it means to the people in each one.
Autocorrelator in photonics
An instrument that measures ultrashort pulse duration by overlapping a pulse with a delayed copy of itself.
The pulse is split in two, one copy is delayed by a scanning mirror, and both are overlapped in a second harmonic crystal; the second harmonic signal versus delay is the autocorrelation trace. Its width is longer than the pulse by a factor set by the assumed shape, 1.41 for Gaussian and 1.54 for sech squared. It gives duration but not phase, which is why FROG and SPIDER exist.
"Autocorrelator says 160 fs assuming sech, but the trace has wings, so get it on the FROG before anyone quotes a number."
Autocorrelator in electronics
An instrument or algorithm that compares a signal with a delayed copy of itself.
This tool measures the degree of similarity between a waveform and a time-shifted version of the same waveform. Engineers use it to extract repeating patterns or fundamental frequencies buried in high levels of random noise. It is heavily utilized in radar, sonar, and advanced signal processing.
"Run the noisy sensor data through the autocorrelator to see if there's a hidden periodic vibration."