A concept to mitigate parasitic self lasing effects in mid-IR fiber amplifiers by means of efficient long period fiber gratings is shown. Using tightly confined ultrashort laser pulses at 800 nm the gratings are directly inscribed into the core of a fluoride glass fiber. Strong attenuation peaks down to −22 dB, with sharp and predictable spectral resonances, were obtained. The gratings reveal great potential to improve the laser performance concerning average output power and attainable spectral range.
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