The purpose of this page is to help Observatories Support Staff and Astronomers to understand and estimate the possible impact of laser contamination on their science program.

A. Summary of the Impact Criteria

The laser light could be seen in:

• the science images recorded in the V and R band.
• in the 589±1 nm region fo the spectra: the laser light could saturate the pixels depending on the exposure time.
• the guiding instrument if working in the V or R band, and when the guide star is fainter than V=12mag.

• infrared imager and spectrograph
• infrared guider
• visible CCDs working shortward of 585 nm.

• About the Laser Guide Star:
  In the upper part of the Earth's mesosphere (90±5 km altitude), there is a 5-15 km thick layer rich in Na atoms, deposited by the ablation of micrometeorites. These atoms can be excited and caused to radiate by sponateous emission by projecting a laser tuned to the Na D atomic transition (589 nm) in the direction of the science target.
  A small fraction of the laser beam light is scattered by dust and air molecules (Mie and Rayleigh scattering) in the lower layers of the atmosphere (~0-30km altitude range). The laser beam will then excites the Na atoms in the 5-15km thick layer at ~90km altitude and produces an artificial star (equivalent V mag. of 8.5<V<10.5), depending on laser power, beam collimation, and Na column density.
• Laser Traffic Control System (LTCS):
  The operating procedures for laser equipped telescopes on Mauna Kea have been established by a working group composed of representatives from several institutions. The rule imposed on Mauna Kea LGS facilities is that a laser equipped telescope must yield (shutter) for a non laser equipped telescope when the non-lasing telescope indicates a sensitivity to laser emissions and a crossing geometry occurs. This page provides more background information on the LTCS. An snapshot of the LTCS status web page is shown here.

• Diffuse, low surface brightness, variable in intensity and direction from the Rayleigh scattering. From digital photography, R. Wainscoat has estimated the Rayleigh background light to be 1.5 and 2.2 magn./(arcsec^2) brighter than the dark sky above Mauna Kea respectively, in the V and R band.
• Brighter emission from the out-of-focus elongated artificial star. There the brightness depends on the separation between telescopes and ranges from 14.4 to 18.8 mag./(arcsec^2) for respectively 80 and 1000 m distance between the telescopes.
  Also, it is noted that telescopes with smaller aperture and/or coaser pixel scales are more affected by laser light contamination (Hayano et al. 2003).