The SDI project was cancelled due to the fact it was extremely expensive, the parts were too large and the Lasers diffracted when they came even close to the atmosphere.
I don't know about any Laser propulsion systems, but I know there is one that is basically a large sail to "catch" the solar wind ( a stream of particles spewed from the sun).
And I figured out how a Photon cannon would work.
When a Photon hits a metal, it can, if it has enough energy, make the electron on a metal atom fly off. Now, IMHO Photon Beam Cannons would be a stream of highly charged Photons that cause the electrons in a metal to be expelled into space, causing the metal to collapse in on itself and make a hole in the targets hull. This also, in theory, works on any material, but it is most efficient on metals.
I am not sure if this would work to bombard a planet though, due to diffraction in te atmosphere.
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"Supernova, ya supernova, supernova goes pop
supernova, ya think it's over but the supernova don't stop" PM5K
Death:"Arnold Judas Rimmer... your life is over. You will travel with me to the-"
#knees death in the groin#
Rimmer:"Remember matey, it's only the good that die young"
"Do not fear the chickens. Become one with the chickens. Respect the chickens and... #BOK!# LEG IT!!!"
The Claw- Project Coordinator and modeller of
Alternate Reality and official spare wheel of The Perfect Storm...