The M2 factor of partially coherent ultrashort pulsed beams

Starting from the space-time Wigner distribution function and taking the Gaussian Schell-model pulsed beam as a typical example, the M2 factor of partially coherent ultrashort pulsed beams is studied. It is shown that the M2 factor increases with increasing bandwidth and decreases with increasing spatial correlation. Furthermore, for chirped pulse, the M2 factor increases as the chirp parameter increases.