05 Sep 2003
Scientists reveal a high power ytterbium laser operating continuous wave at 985 nm.
A team of researchers from France and the US claim to have made a ytterbium laser that emits record continuous wave powers at 985 nm. Sylvie Yiou and colleagues from the Centre Universitaire Paris XI and Lawrence Livermore National Laboratory measured an output power of 250 mW from a Yb-doped S-FAP crystal laser pumped by 1.45 W. (Applied Optics 42 4883)
“This is, to our best knowledge, the highest CW output power ever obtained with a Yb-doped crystal at the wavelength,” say the authors. “This demonstration with a Ti:Sapphire laser is the first step to the diode pumping of an Yb-S-FAP crystal at 900 nm for CW laser emission at 985 nm.”
Laser sources with a good beam quality that emit several watts at 985 nm are needed to pump erbium-doped fiber amplifiers which boost signals in optical networks. Although several solutions already exist, such as semiconductor laser diodes placed in external cavities and distributed feedback lasers, there power output is limited.
According to Yiou and colleagues, another solid-state option is to use a compact Yb-based compact laser. After studying various host crystals, the team settled on an Sr5(PO4)3F or S-FAP crystal because it has a high absorption cross-section. The team also points out that this is a three-level laser transition, which means a high pump-power is required to create a population inversion.
The record-breaking laser uses a 4-mm long cube of Yb:S-FAP containing 1.9 x 1019 Yb ions/cm3. A Ti:Sapphire laser emitting 1.45 W at 900 nm pumps the crystal giving a maximum output power of 250 mW at 985 nm. The authors also report a lasing threshold of 200 mW incident power and a slope efficiency of 20%.