Solid-state dye lasers are far simpler than their liquid counterparts and often expose the researcher to less toxicity. Optical-fiber lasers also offer simplicity as a result of their waveguide makeup. Scientists at Keio University (Yokohama, Japan), Kanagawa Academy of Science and Technology (Kawasaki, Japan), and Polytechnic University (Brooklyn, NY) have combined both in a dye-doped polymer fiber laser. Although solid-state dye-doped fiber lasers have been made before, this version is the first to achieve high efficiency.
A graded-index optical-fiber preform made of poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) and containing 0.1% rhodamine 6G dye by weight was drawn into a fiber with a 0.6-mm core diameter. When transversely pumped with 532-nm light in 1.5-mJ pulses from a frequency-doubled Q-switched Nd:YAG laser, the fiber emitted yellow light in 0.64 mJ pulses, for a slope efficiency of 43% (a comparable bulk solid-state dye laser reached only 7.7% slope efficiency). The experiments were performed at room temperature without external cooling. The output energy of the fiber laser dropped to half its original value after 110,000 pump-laser shots; the researchers ascribe such long life to the protection from oxygen provided by the fiber cladding. The group is investigating other laser-host media and pump-cavity configurations. Contact Yasuhiro Koike at [email protected].