Fiber Laser Produces 4.1 kW

Anne Fischer Lent

Fiber lasers are becoming competitive with traditional flashlamp- or diode-pumped solid-state lasers in applications such as remote sensing, medical surgery and materials processing. Researchers at the University of Manchester in the UK have obtained more than 4.1 kW of 2-µm radiation from a 150-ns, Q-switched Tm³⁺-doped fiber laser.

The active gain medium in a fiber laser is the doped glass core in the fiber. The efficiency of the lasers can be greater than 80 percent, and their large effective surface area and long lengths make them much less sensitive to thermal problems than conventional solid-state lasers. Typically, no active cooling is required.

The study involved different lengths of single-clad fibers with 17-µm-diameter cores, which permitted high power absorption and which were suitable for pumping with the 1.319-µm Nd:YAG laser from Quantronix Corp. A TeO₂ acousto-optic modulator served as the Q-switch, with the laser beam size-matched and aligned to the acoustic signal. They obtained maximum power from a 1.15-m-long cavity.

The researchers observed stimulated Brillouin scattering in the output pulse and recorded as many as 10 orders. Besides high peak power, the laser operated at 30 kHz and displayed a pulse stability of better than 90 percent.

Many companies manufacture fiber oscillators and amplifiers for telecommunications applications, and a handful supply fiber lasers at higher powers and at nontelecom wavelengths, particularly for materials processing and laser marking. The Manchester researchers believe that investigations into fiber lasers will result in more commercial systems, especially for industrial and medical applications.

The next step for the researchers will be to attempt to increase the overall efficiency and to reduce the pulse width to below 150 ns. They also intend to extend the pulse duration to achieve greater pulse energies. By using electro-optic Q-switching, the group has increased the pulse energy by four times in 320-ns pulses.