Lasers that emit light at the sodium line (actually a doublet) at a wavelength of about 589 nm are used to produce artificial “guide stars” in the mesosphere at an altitude of around 90 km for use with adaptive optical (AO) systems integrated with large ground-based astronomical telescopes. These artificial stars allow astronomers to use AO to correct atmospheric aberrations of light passing to and from space. An additional use for this technology is earth-to-space communications.
Now, researchers have developed what they say is an improved laser system for these purposes: a continuous-wave diamond Raman laser emitting at the sodium line. Diamond Raman lasers work by stimulated scattering rather than stimulated emission. The researchers found that this core difference enables the laser to operate more stably at a pure single frequency.
The laser delivered higher power and efficiency than previous guide-star laser systems of its particular type; its characteristics are already competitive with other approaches, but the real significance of the result, say the researchers, is that the technology can be further developed to increase the quality of future guide stars.