Unfortunately, this is far from simple. Laser light is a lossy medium, in that all laser beams diverge.

For example, even just sending a laser to the moon and back is quite sophisticated.

"Laser beams are used because they remain tightly focused for large distances. Nevertheless, there is enough dispersion of the beam that it is about 7 kilometers in diameter when it reaches the Moon and 20 kilometers in diameter when it returns to Earth. Because of this very weak signal, observations are made for several hours at a time. By averaging the signal for this period, the distance to the Moon can be measured to an accuracy of about 3 centimeters (the average distance from the Earth to the Moon is about 385,000 kilometers)." [source: http://www.lpi.usra.edu/lunar/missions/apollo/apollo_11/expe...]

Thus, even if you could get a mirror 25 light years away, the light wouldn't hit it or bounce back.