"Conspiracy theories are big because they're comforting. Any conspiracy is infinitely less multiplex than the real deal, which is multiplex to the point of being unknowable."
- William Gibson

The term "laser cannon" was used earlier. In a 1962 book titled Report on Laser Design Study, we find "results of the design analysis indicate the feasibility of proceeding with the construction of a LASER cannon system at once."

Here's another quote from the Niven/Pournelle 1974 classic Mote in God's Eye:

"Captain, look," he said, and threw a plot of the local stellar region on the screen. "The intruder came from here. Whoever launched it fired a laser cannon, or a set of laser cannon - probably a whole mess of them on asteroids, with mirrors to focus them - for about forty-five years, so the intruder would have a beam to travel on. The beam and the intruder both came straight in from the Mote.

The basic idea for the laser cannon/light sail propulsion system belongs to Robert L. Forward, who published a short paper Ground-Based Lasers For Propulsion In Space in 1961. (Read a short autobiography of Robert Forward.) Dr. Forward gives a more detailed version of the idea in his 1985 novel Rocheworld; see the entry for Interstellar Laser Propulsion System.

Leik Myrabo of the Rensselaer Polytechnic Institute has demonstrated that ground-based lasers can be used to shoot objects into the heavens. The small model craft succeeded in reaching over 100 feet, which compares well to the first test flight of a rocket design by Robert Goddard.

Myrabo's "lightcraft" design is a reflective funnel-shaped craft that channels heat from the laser, towards the center, causing it to literally explode the air underneath it, generating lift.

For more on early uses of solar sail, see the entry from Jack Vance's Sail 25, and starlight sail (light sail) from Cordwainer Smith's The Lady who Sailed The Soul.

The idea of using light pressure to move a spaceship was suggested by Jules Verne in his 1867 novel From the Earth to the Moon; see the entry for light pressure propulsion. The method was explicitly described by Edmond Hamilton in his 1929 short story The Comet Doom; see the entry for ship propelled by light pressure.

See also the launching laser from The Fourth Profession (1971) by Larry Niven.