SEE:
H.R. 5810: Securing Aircraft Cockpits Against Lasers Act of 2010 (GovTrack.us)
Once that passes things will be more clearly defined.
Right Now, the charge, if you hit a plane and are caught, is a Federal Charge of "Interfering with a aircrew in the performance of their duties", or locally, some form of "Disorderly Conduct" charge or similar.
www.faa.gov/documentLibrary/media/Order/7400.2G.pdf
Effectively defines permissible operation of lasers out doors, IE Scientific, Industrial, Display.
FAA wrote 7400.D after a laser show incident in Vegas, in accordance the SAE G10 committee in a advisory role. Its been revised several times.
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=1040.10
Is the basic Federal code enabling the FDA/CDRH to act. Actual guidance is provided by "Laser Letters" and "Laser Notices" which are policy, not a law specifically written by lawmakers. The ability to write and enforce policy is enabled by 21 CFR 1040.
Remember this is Administrative law, not criminal law.
If they really, really want to throw the book at a laser user, there is always the catch-all clause in the Patriot Act, which is PL 107-56.
Don't bother me with the "If its not specifically defined in written law, its not Illegal or its Unconstitutional to charge" argument. That ends at the High School level of interpretation of the law.
The law is a living, breathing thing, and the lawyers have a predictable way of extending it as needed, which is their job.
Steve