Laser wake particle acceleration provides no useful beam luminosity. Space travel is about changing momentum, mv. If your propulsion system involves energy, (mv^2)/2, you are screwed. The better you do the worse you do.

The Starflight Handbook Mallove, Matloff. Nobody is going to be "nearing lightspeed" with any engineering solution including a matter-antimatter drive.

The perfect stardrive would go backward in time as it went forward in space. That way you could go anwhere essentially instantaneously needing only 3 mph (and not endanger schoolchild traffic crossings as you did it).

Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf