'Guide Star' Enables Sodium Measurements

Researchers at Imperial College in London are employing adaptive optics technology to measure sodium in the atmosphere with the 1-m Kapteyn Telescope at La Palma Observatory in the Canary Islands. The continuous-wave output of a 275-mW, argon-ion-pumped ring dye laser is locked to the 589-nm sodium line and launched near zenith, creating a "guide star" that an adaptive optics system would use to quantify atmospheric aberration. The researchers monitor the intensity of the guide star to determine the relative abundance of atomic sodium at mesospheric altitudes of 80 to 110 km.

The laser launch telescope for the project features optical elements from Optical Surfaces Ltd. of Kenley, UK, including a 300-mm aspheric output lens. The company produced the diffraction-limited <f/3 output lens using its proprietary flexible lapping technology.