Is it possible to use a laser to propel a spaceship? Reference: http://adsabs.harvard.edu/full/1968BAN....19..421H
It would be necessary to aim a laser to the target star. How would the density of the laser compare with the interstellar radiation?
Yes, it might be possible to send laser-propelled spaceships to the stars.
There are a whole series of technical challenges in the laser technology and the materials that such a spacecraft might be made of.
The basic idea is to accelerate mini-spaceships with very low mass, but a large, reflective surface area, up to relativistic speeds. The project that I know of is called &quot;Breakthrough Starshot&quot;.
Contrary to what you say in your question, the laser would not be aimed at the target star, it would be aimed at the spaceships! These would have to be set off on a carefully calculated trajectory, because during their decades-long journey, the relative positions of the Sun and target star would change significantly. The impulse phase would take place within the Solar System and the craft would cruise most of the way.
The intensity of the lasers required would be immense compared to the light from a star. The baseline plans involve something like $10^9$ W/m$^2$ delivered to the light sail for 10 minutes. This is to be compared with about $10^3$ W/m$^2$ from the Sun at the orbit of the Earth.