The introductory post on this project mentioned most of the high level considerations for safety and compliance when shooting a laser into the sky. Here, we will go into the gory details.
When lasers will be operated outdoors in the U.S., the Federal Aviation Administration must be given the opportunity to review the safety of the proposed laser operation at least 30 days in advance. Laser beams can potentially affect air traffic and distract or impair pilots during flight, so to mitigate this risk, the FAA reviews the details of the planned operation and responds with a letter of objection or non-objection. The details for how and why to provide this information to the FAA can be found in the Advisory Circular 70-1, with the attached forms “Notice of Proposed Outdoor Laser Operation(s)” and “Laser Configuration Worksheet.” Note that if the laser operations are for entertainment as opposed to scientific use, the Food and Drug Administration must be notified in addition to the FAA.
Beyond the basic information such as date and time of operation, site latitude, longitude, and elevation, etc., it is necessary to calculate and provide energy density values at various distances from the laser’s origin. Every laser diverges to some extent, so that its beam spreads out and becomes less bright over distance. The divergence of a laser is measured in milliradians, which is an angle measurement (1° ≈ 17.45 mrad). The amount of energy in the laser beam stays relatively constant over distance, so as it diverges, the density of the energy decreases. In other words, the amount of energy per unit of area in the cross section of the beam decreases as you take cross sections farther and farther from the laser’s point of origin.
Read more, cool to see there are ways to do cool stuff and work within reasonable rules.
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