FIGURE C.1 Progress in output power for 1 µm, 1.5 µm, and 2 µm optical amplifiers. This plot tracks the historical progress in output power from a single fiber amplifier. Ytterbium (Yb)-fiber amplifiers (1 µm) have a significant lead over other technologies primarily due to their low quantum defect and the abundance of high-brightness pump sources at 915 to 975 nm. However, thulium (Tm)-fiber amplifiers (1.9 to 2.1 µm) have been demonstrated with average output powers approaching 1 kW and pulsed operation approaching 100 kW without sacrificing beam quality. There are several commercial units available with an average power ∼150 W. Their efficiency is set by the efficiency of the pump source, which should continue to improve over time as demand for Tm-lasers increases. SOURCE: Cristensen, S., G. Frith, and B. Samson. 2008. “Developments in Thulium-Doped Fiber Lasers Offer Higher Powers.” SPIE Newsroom. DOI: 10.1117/2.1200807.1152. Available at http://spie.org/x26003.xml. Reprinted with permission.
commercial amplifiers is approximately 6.25 percent6 limited by the efficiency of the pump source. However, there have been many investments made in these areas, which should improve the efficiency over time.