Improved laser system will help large optical telescopes gather more accurate data

https://phys.org/news/2020-04-laser-large-optical-telescopes-accurate.html

Macquarie University researchers have developed an improved laser system that will help large optical telescopes to gather more accurate data.

Large-diameter ground-based optical telescopes now routinely use laser-beam generated artificial guide stars, created in the higher levels of the atmosphere. These artificial stars allow users to correct atmospheric aberrations of light passing to and from space, using adaptive optics. They are crucial for high fidelity transmission of data for applications in both optical free-space and ground to earth communications, in space debris imaging and tracking, and for astronomy.

The principle involves using a precisely tuned laser to energize atoms in the sodium layer that occurs naturally in the mesosphere, at an altitude of around 90 km. These atoms re-emit the laser light, temporarily creating a glowing artificial star. There have been a number of technologies developed to do this, but generating that specific wavelength has been a notorious challenge that has so far needed impractical approaches.
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the paper:
https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-7-1898

Diamond sodium guide star laser:

Abstract:

Laser guide stars based on the mesospheric sodium layer are becoming increasingly important for applications that require correction of atmospheric scintillation effects. Despite several laser approaches being investigated to date, there remains great interest in developing lasers with the necessary power and spectral characteristics needed for brighter single or multiple guide stars. Here we propose and demonstrate a novel, to the best of our knowledge, approach based on a diamond Raman laser with intracavity Type I second-harmonic generation pumped using a 1018.4 nm fiber laser. A first demonstration with output power of 22 W at 589 nm was obtained at 18.6% efficiency from the laser diode. The laser operates in a single longitudinal mode (SLM) with a measured linewidth of less than 8.5 MHz. The SLM operation is a result of the strong mode competition arising from the combination of a spatial-hole-burning-free gain mechanism in the diamond and the role of sum frequency mixing in the harmonic crystal. Continuous tuning through the Na D line resonance is achieved by cavity length control, and broader tuning is obtained via the tuning of the pump wavelength. We show that the concept is well suited to achieve much higher power and for temporal formats of interest for advanced concepts such as time-gating and Larmor frequency enhancement.