The cover article in the March 2017 issue of Scientific American was about using multiple light sails and miniature sensors to visit Alpha Centauri, with a large array of lasers -- either earth-based or space-based -- as the primary accelerant. The use of light sails, however, can be problematical.
First of all, consider solar wind, the stream of gases and particles emitted by the sun. If solar wind is faster than the sails, it will accelerate them beyond the force of the proposed laser array. If the solar wind is slower than the sails, however, the sails will decelerate. In either case, the solar wind and the sun's gravity can alter the trajectory of the sails.
The Oort cloud also requires consideration. If the sails are not punctured by the particles in the Oort cloud, impacts of those particles on the sails will decelerate them. If the sails are punctured, they will become useless in decelerating the sensors when the target star is approached.
Then there is the fact that space is not a perfect vacuum. Without dark matter, space still contains gas and dust, which can decelerate the sails. If dark matter does indeed pervade space, the deceleration might be sufficient to prevent the sails and their sensors from ever reaching their target stars.
This does not make the concept of light sails impossible. Before such a project is launched, however, more knowledge is needed about the solar wind, the Oort cloud, and what exists in space between here and any target star.