I made in https://news.ycombinator.com/item?id=28003977 a back of the envelope calculation using the laser that NASA use to measure the distance to the Moon. It's a pulsed laser that fires in a very short time, and it use a very narrow band. If you use it to communicate with other star, the light of the Sun in this band is like 10^8 times stronger. For a wide spectrum signal, you have an even higher noise level.