This is the version as it was used by Team Monkey Business to win the 2015 (DEFCON 23) competition.
The turret hardware consists of an Arduino 2560 board, RAMPS 1.4 controller, two NEMA 17 stepper motors, a couble of end-stop switches, Microsoft webcam, and the laser prescribed below.
The laser used for the contest is the 50 mW version of this laser: http://www.civillaser.com/532nm-5mw50mw-ttl-modulation-green-laser-module-dot-16mmx70mm-p-130.html
You'll need a controller to run the robot. The source for the controller can be found in the /hw folder.
Software to run the reference robot is in the /sw/TowerDefenderMkII folder.