Ultrashort Laser Pulse Phenomena, 2nd Edition

Interferometric Correlations 459

It is therefore important to consider the limit where the signal itself has to be

used as reference. The expression (9.1) with I

s

(t) = I

r

(t) = I(t)iscalledan

intensity autocorrelation. An autocorrelation is always a symmetric function—

this property can be understood from a comparison of the overlap integral for

positive and negative arguments τ. According to Eq. (9.3), the Fourier transform

of the autocorrelation is a real function, consistent with a symmetric function in

the time domain. As a result, the autocorrelation provides only little information

on the pulse shape, because an infinity of symmetric and asymmetric ...