Laser sources operating at the 1.2 μm wavelength band have some unique applications in photodynamic therapy, biomedical diagnosis and oxygen sensing. Additionally, they can be adopted as pump sources for mid-infrared optical parametric generation as well as visible light generation by frequency doubling. Laser generation at 1.2 μm waveband has been achieved with different solid-state lasers including semiconductor laser, diamond Raman laser, and fiber laser. Among these three types, fiber laser thanks to its simple structure, good beam quality, and operation flexibility, is a great choice for 1.2 μm waveband laser generation.
Researchers led by Prof. Pu Zhou at National University of Defense Technology (NUDT), China, are interested in high power fiber laser at 1.2 μm waveband. Current high power fiber lasers are mostly ytterbium-doped fiber lasers at 1 μm waveband, and the maximum output at 1.2 μm waveband is limited at ten-watt level. Their idea is to use stimulated Raman scattering effect in passive fiber to obtain high power laser generation at 1.2 μm waveband. Stimulated Raman scattering effect is a kind of third order nonlinear effect which convert photons into longer wavelength. By utilizing stimulated Raman scattering effect in phosphorus-doped fiber, the researchers convert high power ytterbium-doped fiber at 1 μm waveband into 1.2 μm waveband. A Raman signal with power up to 735.8 W at 1252.7 nm is obtained, which is the highest output power ever reported for fiber lasers at 1.2 μm waveband. The work entitled "High power tunable Raman fiber laser at 1.2 μm waveband" was published on Frontiers of Optoelectronics (published on Jan. 15, 2024).
