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We report the observation of a new regime of operation in the stretched-pulse fiber laser in which two groups of bound pulses travel in the cavity at different velocities. The pulse groups collide periodically and remain apparently unaltered after the collisions. The observed group-velocity difference is shown to exhibit a strong dependence on the time interval between the pulses in each bound state.

This work presents the proof of concept of a remote sensing system designed for the detection of molecular species such as gas pollutants via active differential optical absorption spectroscopy in the short-and mid-wavelength infrared. The system includes an optical parametric generator generating broad linewidth pulses tunable between 1.5 and 3.8 μm. A telescope coupled to a grating spectrograph and an in-house gated HgCdTe avalanche photodiode measures the whole return spectrum from each pulse. Experiments show simultaneous detection in atmospheric air and inside a cell of H 2 O and CO 2 at 2 μm, and H 2 O and CH 4 at 3.3 μm. The detection limits for CO 2 and CH 4 are 158 and 1 ppm·m, respectively. A new algorithm is also presented enabling the determination of concentrations when spectra include strong absorption features.