Doubled fiber laser creates yellow light

Tue 21-02-2006
A frequency-doubling technique promises more efficient, cheaper and more reliable yellow light.

Researchers at Stanford University, US, say they have come up with a way of generating coherent yellow light, which may eventually help in treating people with eyesight and skin disorders (Optics Letters 31 347).

"Our goal was to amplify a master oscillator and then double the frequency to generate watts of yellow," lead researcher, Supriyo Sinha, told "We believe our approach has several advantages over other approaches to generating yellow." The team generated 40 mW at 575 nm by directly frequency doubling an 1150 nm fiber laser. The gain medium was a ytterbium-doped silica fiber and the frequency doubling was done using a lithium niobate (PPLN) waveguide. The medical yellow laser systems in-use today are based on dyes, which are sometimes toxic, or copper-vapour lasers, which take time to heat up to high temperatures.

These disadvantages have led to researchers world-wide looking for yellow solid-state based lasers, which offer potentially lower commercial costs, higher compactness and greater reliability.
Alternative ways of generating solid-state yellow coherent light include Sum Frequency Generation (SFG) of two lasers. A second method includes Raman shifting a laser gain in fiber and then frequency doubling the output.
According to Sinha, the new method uses fewer components than an SFG system, produces much narrower linewidths than Raman shifting and also allows greater pulse-width flexibility than the other techniques.
"We are now looking at two objectives with regards to this project: firstly, to efficiently amplify the oscillator to many watts of output power at 1150 nm, and secondly, to extend the concept to 1178 nm, doubling to sodium yellow (589 nm)," added Sinha.