Product of temporal and Spectral Width of a pulse.

The time-bandwidth product of a pulse is the product of its temporal duration and spectral width (in Frequency space). In ultrafast Laser physics, it is common to specify the full width at half maximum (FWHM) both in time and frequency domain. The minimum possible time-bandwidth product is obtained for bandwidth-limited pulses. For example, it is ≈0.315 for bandwidth-limited sech2-shaped Pulses or ≈0.44 for Gaussian-shaped pulses. This means e.g. that for a given spectral width, there is a lower limit for the pulse duration. This limitation is essentially a property of the Fourier transform.