For professionals using lasers outdoors
(observatories, remote sensing, light shows, etc.)
If you use lasers in airspace professionally, then you are probably already aware of the need to avoid aircraft. In the U.S., the Federal Aviation Administration asks outdoor laser users to submit details of their laser use. This process is described in more detail on the Rules for U.S. outdoor users page.
Apache Point Observatory lasing the Moon (overexposed)
during an Apollo lunar laser ranging experiment.
Photo by Dan Long taken at 11:30 pm local time, via Wikipedia.
Aircraft spotters
The FAA first became involved with outdoor laser uses in the 1980s and early 1990s. Since that time, they have permitted laser use if aircraft spotters are used. Spotters watch that the beam does not get too close to the beam. Usually a spotter either can turn off the beam directly, or can radio to an operator who then turns off the beam. (The laser itself is normally left on, but the beam is stopped from going into airspace. This is called “termination”.)
For short-term occasional uses such as laser light shows, spotters are sufficient. Spotters may well be sufficient for your uses.
However, some users such as observatories use lasers most of the night, often at high altitudes where the air is cold and thin. Hiring spotters and having to relieve them every hour or so can be expensive.
Automatic or semi-automatic aircraft detection
Therefore, a number of organizations have proposed solutions involving radar or other means to turn off the beam. The termination command can be done automatically, or by an operator who is monitoring the radar from a comfortable location indoors or even miles away from the laser site.
As of 2009, the FAA has not given full permission to any automated or semi-automated system. Such permission is likely within a year or two. Professionals using lasers outdoors should keep abreast of this topic.
Limitations imposed by U.S. Air Force rules
A 2008 study by the U.S. Association of Universities for Research in Astronomy noted that rules imposed by the U.S. Air Force are beginning to restrict scientific research. Air Force Space Command asks observatories to not use lasers at times and places when satellites with sensitive sensors are passing overhead. This used to be on the order of a dozen “do not fire” events per night; now it can be hundreds per night. The conflict between research and military necessity received public attention in October 2009 with a New Scientist article, Astronomers clash with US air force over laser rules, and one in Physics Today, “Adaptive optics restrictions placed on astronomy”.
Resources
SAE G10T Laser Safety Hazards Subcommittee. The SAE G10T industry group has a document about outdoor laser control measures, and is providing guidance to FAA in this area. If you are interested in automated control measures, you should contact some of the astronomy or other industry members of this group.
How to Keep Planes From Colliding With Lasers, a general interest article from Wired about a dual-radar system developed by the University of California in San Diego. It uses two radar beams, one wide angle and one narrow angle, to determine when an aircraft is within about 15 degrees of the laser beam. They have tested at two observatories and posted their results online. (Links are within the article.) This information can also be found online at Softpedia, “New System Shuts Down Lasers When Airplanes Appear”.