Another great resource for hypothetical space stuffs (with math!) is Atomic Rockets / Project Rho, here's some of their articles on laser propulsion:
https://www.projectrho.com/public_html/rocket/enginelist.phpYeah that’s a fantastically deep site. After reading the torch ship chapter I’ve come to the conclusion that we either are alone in the observable universe or we’ll be forever bound to our solar system, because we’d see fusion drive signatures on sky surveying telescopes if both are false.
Or, we're missing some corner of physics that allows for interstellar travel that doesn't leave obvious signatures (or misunderstanding a signature that is present).