Hi Scott

You're right about the reaction force - for a realistic manned starship the reaction will be huge. The laser bank will need to be anchored on an asteroid or dynamically supported against the reaction - for example a sunlight-supported solar collector would be pushed back only enough for the force to then be equalled by the opposing sunlight.

An alternative to reaction via photon pressure is to use a laser to accelerate mini-sails that are blasted into plasma by lasers on the starship. These mini-bursts of plasma then push against a magnetic field generated by the starship providing forwards thrust.

Here's a good article from Andrews Aerospace...

Publications

...click on the article titled "Interstellar Transportation" for the PDF download to start. It covers a number of propulsion options, opting for the laser mini-sail system I've described - developed by Jordin Kare - as the most easily achieveable.

Adam