Raman laser

A team of US scientists claims to have made the world's first electrically-driven Raman laser, a development that could lead to a new type of semiconductor laser operating at wavelengths that conventional laser chips cannot reach.

Although lasers that rely on Raman scattering (a nonlinear optical effect that amplifies light signals) have been demonstrated before, so far they have always required a powerful external laser to pump them.

Federico Capasso, one of the inventors of the quantum cascade laser, and his co-workers from Harvard University, Texas A&M University and Bell Labs have now come up with a solution that gets around the problem.

The design exploits Raman scattering between quantum wells within the active region of a QCL to produce a very compact semiconductor Raman laser.

When electrically-pumped, the QCL starts to lase and its emission at 6.7 µm is Raman shift to 9 µm.

The laser itself is microscopic - about 10 µm wide, 6 µm thick and 2 mm long.

By carefully designing the structure of their InGaAs/InAlAs QCL, the team says it can achieve highly efficient Raman conversion of around 30%, which is orders of magnitude stronger than that usually observed in silica optical fibres.

So far, the team has made 10 samples and achieved Raman lasing in all of them.

Its prototypes emit just under 20 mW at a drive current of 4 A and operate at temperatures of up to 170 K.

The researchers now plan to increase the temperature of operation and demonstrate lasing at other wavelengths.