Pulse duration ($\tau$)

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.^[ref]

For an original example, choose a triangular power pulseIts 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.