Generation and direct measurement of giant chirp in a passively mode-locked laser

We evaluate the shape and chirp of nanosecond pulses from a fiber laser passively mode locked with a nanotube-based saturable absorber by using a synchronously scanning streak camera and a monochromator to directly measure the pulse spectrogram. We show that the stable sech(2) output pulse possesses a predominantly linear chirp, with a residual quartic phase and low noise. Comparison with analytical mode-locking theory shows a good quantitative agreement with the master equation mode-locking model.