Thulium-based 2 μm fiber laser reaches 200 MW peak power

Jan. 7, 2015
A team from Germany has developed a thulium (Tm)-based fiber-laser system that produces a peak pulse power of more than 200 MW, a pulse energy of 12 μJ, and a 24 W average power.

Lasers emitting at around 2 μm are useful for their eye-safe qualities (remote sensing) and other purposes (IR spectroscopy, supercontinuum generation, and materials processing); as for almost any other laser-emission wavelength, scientists and engineers using these lasers are often looking for more laser power and or pulse energy at 2 μm. A team from Friedrich-Schiller-Universität Jena and the Fraunhofer Institute for Applied Optics and Precision Engineering (both in Jena, Germany) has helped to fulfil these needs by developing a thulium (Tm)-based fiber-laser system that produces a peak pulse power of more than 200 MW, a pulse energy of 12 μJ, and a 24 W average power.

The chirped-pulse-amplification (CPA) system includes a Tm-doped fiber with a mode-field diameter of 65 μm, efficient dielectric gratings, and a Tm-based fiber oscillator. The fiber oscillator, which operates in the stretched-pulse regime and emits 1.2 nJ pulses at a 24 MHz repetition rate, accomplishes stable mode-locking by taking advantage of nonlinear polarization changes; it is a self-starting oscillator relying on a saturable-absorber mirror. The stretcher and compressor are enclosed in low-humidity boxes to minimize light loss from water-absorption lines; the compressor gratings have a diffraction efficiency of more than 98% and a compressor efficiency of more than 80%. The large-pitch-fiber amplifier is directly water-cooled and counter-pumped with light from a 790 nm laser diode. Future use of a vacuum or nitrogen atmosphere in various parts of the optical path could reduce thermally induced beam degradation as well as nonlinear effects; larger mode-field areas will lead to even higher powers. Reference: Fabian Stutzki et al., Opt. Lett. (2015); http://dx.doi.org/10.1364/OL.40.000009.

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