Fiber Delivery Is Tested for High-Power Lasers

YOKOSUKA, Japan -- The demand for high-power lasers in industry and medicine has continued to grow, sparking studies on more effective and efficient delivery systems. Re-search teams in Japan and in Israel independently reported in the May issue of Optical Engineering that they have used optical fibers to deliver high-power, mid-IR laser light, opening possibilities in surgical and industrial welding applications.
The Japanese researchers, headed by Satoshi Tanaka of the National Defense Academy, examined As₂S₃ optical fiber with a carbon monoxide laser that they built in their laboratory. The Israeli team, led by Ben-Zion Dekel of Tel Aviv University, investigated the use of hollow glass waveguides and silver halide fibers for CO₂ laser systems.
Tanaka's team chose the CO laser over the CO₂ because, he said, its 5.3-µm output can be focused more efficiently and optical devices can be attached more easily. However, this laser is not commercially available. Tanaka also noted the high cost of building a CO laser, the danger that CO gas presents to users and the fact that the gas must be cooled for high-power operation.
The Japanese team inserted a pigtail As₂S₃ optical fiber directly into a 0.6-mm coupling hole in one of the optical resonator's mirrors. As long as the loops of the pigtail were larger than 22 cm, the fiber was as efficient as a straight one.
The group extracted approximately 60 W from the setup. "Sixty watts from a CO laser corresponds to about 400 W from a CO₂ unit," Tanaka said. He noted that the shorter wavelength of the laser results in a higher power density and that the flexibility of the pigtail fiber enables the setup to be used by computer-controlled robots and in automated noncontact machinery.
Dekel's team applied two-dimensional magnetic fields on the marking tip of a CO₂ laser to focus the beam through either hollow silica glass waveguides or silver halide polycrystalline fibers. He said that both appear promising but that they are still limited to use with output less than 50 W. "They must be improved before they can have commercial applications," he said.