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

Abstract

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.

Mode-Locked Fibre Lasers with High-Energy Pulses

“…Chen et al, 2009;Nyushkov et al, 2010;Kobtsev et al, 2010a;Ivanenko et al, 2010). In particular, demonstrated experimentally in (Kelleher et al, 2009) were 1.7-ns-long pulses with a giant chirp generated in 1,2-km-long fibre laser mode-locked due to nanotube-based saturable absorber. The time-bandwidth product was about 236, which was ~750 times the transform limit, assuming a sech 2 profile.…”

“…Schematic of extra-long mode-locked fibre laser: F2 -All-wave fibre, length of 2,6 km. New results obtained in the experiments (Kobtsev et al, 2008c) with relatively high energy of pulses directly in a passively mode-locked laser stimulated further investigations in this area Zhang et al, 2009;Lin et al, 2011;Song et al, 2011;Ai et al, 2011;Kobtsev et al, 2009;Senoo et al, 2010;Kelleher et al, 2009;L. Chen et al, 2009;Nyushkov et al, 2010;Kobtsev et al, 2010a;Ivanenko et al, 2010).…”

“…Thus, the results discussed above indicate a gradual decrease in the stability of lasing associated with a corresponding increase in the cavity length. Stable single-pulse mode-locked lasing can hardly be achieved in an NPE laser with a cavity length exceeding 100 m. However, the experiments reported by (Kelleher et al, 2009) show single-pulse lasing in a cavity longer than 1 km when a saturable absorber is used for mode locking. But even in this case, the question of compressibility of pulses characterised by a giant chirp remains open.…”

“…Another problem related to pulse compression is the absence of linear chirp in a number of generation modes. For instance, although (Kelleher et al, 2009) reports experimentally observed 1.7-ns-long pulses with giant chirp generated in 1.2-km-long fibre laser modelocked due to nanotube-based saturable absorber, compression of pulses generated in NPE lasers is far from being possible in all the generation regimes. Our experiments and numerical modelling indicate that efficient pulse compression is only possible in a stable generation mode, whereas pulses observed in quasi-stochastic modes of wave packet generation are not easily compressible.…”

Generation of 1.7-μJ pulses at 1.55 μm by a self-mode-locked all-fiber laser with a kilometers-long linear-ringcavity

“…A gigantic chirp of generated pulses, which increases with the cavity length, may be considered as a drawback of this approach. However, it has been experimentally discovered that this chirp is predominantly linear [7]. This feature allows presuming that an efficient pulse compression is possible.…”