= Pulse duration
{title2=$\tau$}
\b[Pulse duration] quantifies a pulse's temporal extent using a stated observable and width convention. A common optical convention is the <full width at half maximum> of the background-subtracted <radiant power> profile. The Ansys source documentation explicitly defines its PULSELENGTH parameter as the power-profile FWHM, rather than the width of the electric-field amplitude.<Plane wave and beam source - Simulation object in Ansys Optics documentation>[Frequency/Wavelength tab, Standard source PULSELENGTH definition]{ref}
For an original example, choose a triangular power pulse
$$
P(t)=P_{\rm pk}\max\left(1-\frac{|t|}{T},0\right),\qquad T=8\,\mathrm{ns}.
$$
Its nonzero support extends from $-T$ to $T$, giving total support width $16\,\mathrm{ns}$. Its half-maximum crossings occur at $t=\pm T/2$, giving a power FWHM of only $8\,\mathrm{ns}$. Neither number is wrong when its convention is specified. The <pulse energy shape factor> additionally relates a chosen width to integrated energy and <peak power>.
A fast <photodetector> and <oscilloscope> record an electrical response to an optical pulse. For a linear response model, the recorded trace is a <convolution> with the instrument's <impulse response>; a slow response can broaden the measured feature. The readout width need not equal the optical width. State the observable, background treatment and instrument response when reporting a duration. <Pulse energy baseline correction> affects where the half-maximum threshold lies, while <Gaussian pulse energy and peak power> treats the conversion for a specific power-profile family.
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