Increasing the output of 2-micron silicate fiber lasers using nanoparticle doping
Abstract
Kilowatt-class directed energy fiber lasers have been realized based on Yb- and Tm-doped silica glasses. Yb lasers operate at 1-microm and have yielded the highest output powers (>10 kW) and efficiencies (currently >85%) to date. Fiber lasers employing Tm can operate at 2-microm, which is considered an eye-safer spectral region and has driven considerable research and commercial efforts. However, there are currently significant problems with Tm-ion based fiber lasers systems. Efficient 2-microm emission from Tm requires high doping concentrations to facilitate cross-relaxation (CR, initially developed in silica fiber by PI Jackson (1)), which (theoretically) provides 2 emitted (laser) photons for each (790 nm) pump photon absorbed above laser threshold. The glass science of silica requires large Al doping levels to minimize clustering of the Tm ions, which leads to quenching (1) from energy transfer upconversion (ETU). Accordingly, Tm fibers possess combined (Tm+Al) concentrations that are near the stability limits for silica glass while also raising the refractive index, necessitating complex pedestal designs to promote spa􀆟ally single (or low) molded operation. Furthermore, since Tm exhibits lower maximum slope efficiencies (approximately 60%) and higher pump absorption because of the high Tm doping, Tm fibers experience at least an order of magnitude higher thermal loads per length of fiber than does Yb. Accordingly, when compared to Yb, these characteristics translate into Tm fibers being more expensive and complicated to make. The corresponding lasers require extravagant thermal management because of the higher thermal load densities in the fiber. Despite all this development, Tm fiber lasers still produce much lower output power compared to Yb.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 05, 2025
- Source ID
- FA95502410026
Entities
People
- John Ballato
Organizations
- Air Force Office of Scientific Research
- Clemson University
- Office of the Secretary of Defense