Femtosecond (fs) mid-infrared (mid-IR) laser sources emitting within the atmospheric window from 3 to 5 μm are of broad interest for remote sensing and spectroscopic applications, for their ability to access the fundamental rotational-vibrational absorption features of many gas-phase molecules. Rare-earth doped fluoride fibers have shown great potential as active media for fs laser sources in the mid-IR. In particular Dy3+ possesses a broadband emission from 2.8 to 3.4 μm that can be beneficial for ultrafast pulse generation and amplification. Generation of 30-ps mode-locked pulses has been demonstrated by frequency shifted feedback method in a linear configuration . Here we present a passively mode-locked Dy3+-doped fluoride fiber laser emitting around 3.1 μm based on nonlinear polarization evolution (NPE) technique in a ring configuration, using in-band pumping at 2.8 μm, able to produce sub-picosecond (ps) pulses .
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