Calculating the velocity and timing some external actuator sounds easy enough. But getting the 'light curtains' working, and creating the hardware to 'fire a board' both sound potentially tricky.
I've seen videos of various systems that solve this problem optically (using 3-D ball tracking techniques) but they do look rather complex. If you only want something that will bounce the ball back with a bit of energy added, I suspect your simplest bet would be to put a touch sensor on the board or your 'light curtain' just in front of the board and use that to trigger some sort of high force mechanism that knocks the board forward. And I'd probably do [u]that[/u] by having it restrained against some springs with a trigger mechanism to release it suddenly, then slowly wind it back against the springs for next time.