We report a passively mode-locked Dy 3 :fluoride fiber laser emitting around 3.1 μm based on the nonlinear polarization evolution technique in a ring configuration, using in-band pumping at 2.8 μm. Transform-limited and selfstarting mode-locked pulses as short as 828 fs with a center wavelength around 3.1 μm and repetition rates up to 60 MHz are obtained. In the single-pulse regime, a maximum average output power of 204 mW is measured, corresponding to a peak power of 4.2 kW and a pulse energy of 4.8 nJ. This first demonstration, to the best of our knowledge, of a femtosecond mode-locked fiber laser emitting directly beyond 3 μm paves the way for frequency comb synthesis in the molecular fingerprint region.
We report, to the best of our knowledge, the first entirely monolithic dysprosium (Dy)-doped fluoride fiber laser operating in the mid-IR region. The system delivers 10.1 W at 3.24 μm in continuous operation, a record for fiber oscillators in this range of wavelengths. The Dy 3+ fiber is pumped in-band using an erbium-doped fiber laser at 2.83 μm made in-house and connected through a fusion splice. Two fiber Bragg gratings directly written in the Dy-doped fiber form the 3.24 μm laser cavity to provide a spectrally controlled laser output. This substantial increase of output power in the 3.0 3.3 μm spectral range-could open new possibilities for applications in spec-troscopy and advanced manufacturing. There is considerable interest in developing high-power mid-IR coherent sources to enable novel applications across a broad range of disciplines. Sources operating in the 3-4 μm spectral range currently find applications in spectroscopy as they can directly probe the fundamental stretch resonances of molecular bonds such as C-H and N-H. This feature makes them a key component for sensing a variety of combustion gases [1], including hydrocarbons [2], as well as various types of explosive materials (e.g., TNT, RDX, PETN, etc.) [3]. The overlap with these strong molecular resonances can also be highly valuable in the advanced manufacturing sector, for instance, to efficiently process polymer materials [4,5].
We report, to the best of our knowledge, the first demonstration of a gain-switched fiber laser operating near 3.5 μm. A dual-wavelength pumping scheme consisting of a 1976 nm Q-switched fiber system and a continuous-wave 976 nm laser diode were used to gain-switch a monolithic erbium-doped fluorozirconate fiber laser cavity at 3.552 μm. Stable pulses were produced for repetition rates ranging between 15 and 20 kHz, and a record peak power of 204 W was achieved at 15 kHz. A quenching phenomenon was also observed at 15 kHz for 1976 nm pulse energies beyond 180 μJ.
Mid-infrared fiber sources, emitting between 2.5 µm and 5.0 µm, are interesting for their great potential in several application fields such as material processing, biomedicine, remote sensing and infrared countermeasures due to their high-power, their diffraction-limited beam quality as well as their robust monolithic architecture. In this review, we will focus on the recent progress in continuous wave and pulsed mid-infrared fiber lasers and the components that bring these laser sources closer to a field deployment as well as in industrial systems. Accordingly, we will briefly illustrate the potential of such mid-infrared fiber lasers through a few selected applications.
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