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Fiber lasers enter kilowatt regime

22 Dec 2004

A single strand fiber laser emits more than 1kW of continuous wave power.

Researchers from the University of Southampton, UK, claim to have developed the most powerful fiber laser, based on a single strand of fiber, to date. Their cladding-pumped ytterbium-doped design emits 1.36 kW of continuous-wave output at 1100 nm. It also boasts a slope efficiency of 83% and near diffraction-limited beam quality. (Optics Express 12 6088).

Although fiber lasers that generate higher powers have already been demonstrated, they rely on combining the output from a bundle of several fibers.

As the Southampton scientists explain in their paper, the rapid progress in doped single-fiber lasers has been fuelled by the exceptional ability of fibers to carry high optical power and by the availability of powerful diode lasers for use as pumps.

With applications such as welding, cutting and marking of metals and ceramics, there is a potentially large market for high-power, compact and robust solid-state fiber-laser sources. However, their success as a replacement for conventional industrial lasers depends on being able to achieve high beam quality.

The Southampton ytterbium-doped single-fiber design has a beam quality factor (M2) of 1.4, indicating that the beam is nearly diffraction limited. With power conversion efficiencies of greater than 80%, silica-based ytterbium-doped fibers are strong contenders for high power sources.

Drawn from a preform made in-house using modified chemical-vapor-deposition and solution-doping, the fiber has a 40 micron diameter ytterbium-doped aluminosilicate-based core and a numerical aperture below 0.05.

In a double-ended scheme, the researchers pump their 12 m double-clad fiber with two 975 nm diode stack sources generating 1.8 kW of total pump power. With no evidence of roll-over in laser output power, even at the highest pump power, the team is predicting big things for the road ahead.

“Power-scaling beyond 10 kW in a single-fiber configuration looks entirely feasible with our fiber laser design,” say the authors in their paper. “We expect to achieve diffraction-limited beam quality with a comparable or higher output power in the near future through more advanced fiber design, combined with more powerful pump sources.”

According to David Parker, CEO of University of Southampton spin-off Southampton Photonics (SPI), SPI will be commercializing the kilowatt laser technology for industrial and aerospace applications requiring compact and reliable kilowatt sources. The work was funded by the Defence Advanced Research Projects Agency (DARPA), US, under its high-power fiber laser program.

James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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