High power tunable ultrafast fiber laser emitting above 3 μm

Summary form only given. Upcoming applications in material processing, countermeasures, remote sensing and spectroscopy will rely on the development of simple and reliable sources that generate intense laser pulses in the mid-IR spectral region (3-20 μm). Fiber lasers are certainly among the most promising candidates for such applications. Mid-IR ultrafast fiber lasers have been recently demonstrated using Er<;sup>3+<;/sup>- and Ho<;sup>3+<;/sup>-doped fluoride glass fibers [1, 2]. However, the emission spectra of these soliton fiber lasers are currently limited to wavelengths below 3 μm. The energies and peak powers of the generated pulses also remain modest (respectively <; 7 nJ and <; 50 kW) as compared to existing mid-IR solid-state laser systems based on parametric conversion.Here, we present a SSFS-based ultrafast fiber laser with record output performances in the mid-IR. As shown in Fig.1 a), femtosecond solitons at 2.8 μm generated from a mode-locked fiber oscillator (described in [1]) are launched in a double-clad erbium-doped fluorozirconate fiber. The first segment of fiber is pumped at 980 nm and thus acts as an amplifier. After this short segment, the remaining of the pump is stripped via a cladding mode stripper (CMS). While the solitons are slightly shifted during the amplification, SSFS mainly occurs in the long unpumped segment following the amplifier. This laser source generates sub-200-fs pulses with energy up to 37 nJ and peak power up to 200 kW [4]. The output pulses can be shifted from 3 μm up to 3.6 μm depending on the length of the unpumped segment. Spectral tunability is controlled by varying the input pump power in the amplifier. The high repetition rate (58 MHz) of this laser source allows for the generation of watt-level output powers over the whole tuning range.