= Isolated attosecond pulse
An <isolated attosecond pulse> has one dominant short burst within the observation window, with any satellite emission quantified. A broad <optical spectrum> alone cannot distinguish one burst from several. Selecting a generation interval and an appropriate spectral band can suppress neighboring bursts, but the resulting temporal contrast must still be tested.
For a simple calculation independent of any apparatus, let $\mathcal E(t)=f(t)+r e^{i\theta}f(t-\Delta)$, with two nonoverlapping copies of a short <optical pulse>. Its <optical spectrum> has intensity
$$
|\widetilde{\mathcal E}(\Omega)|^2
=|\widetilde f(\Omega)|^2\left[1+r^2+2r\cos(\Omega\Delta+\theta)\right].
$$
A satellite produces spectral fringes of angular spacing $2\pi/\Delta$ when the two bursts are coherent and resolved. For chosen field-amplitude ratio $r=0.2$, the satellite/main <energy> ratio is $r^2=0.04$, while fringe visibility is $2r/(1+r^2)\simeq0.3846$. Weak satellite <energy> can thus leave substantial fringes. Averaging an uncontrolled $\theta$ removes the interference term without removing the satellite: absence of fringes alone does not prove isolation.
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