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.
Always state the deconvolution factor with an autocorrelation result: the same trace gives a different pulse duration for each assumed shape.
Also heard as
- AC
Related terms
Pulse duration
How long a laser pulse lasts, normally given as the full width at half maximum of its intensity.
SHG
Second Harmonic Generation: converting light to exactly double its frequency, half its wavelength, in a nonlinear crystal.
Transform-limited
Describes a pulse that is as short as its spectral bandwidth allows, with no leftover chirp.
Pedestal
A low, broad background of light under or around an ultrashort pulse, which carries energy outside the main peak.