The physics doesn't stack up for me. The spacecraft must be lightweight so it can be accelerated to high speeds but it must also have a very large area such that a large proportion of the laser photons hit it. This means a very thin disc shaped spacecraft (a few grams but with a few m2 of area). Whilst this may be able to be constructed it would be incredibly delicate for launch and I can't see how it would have the required strength to avoid it tearing apart under the force applied by the laser photons.
>A critical issue will be the stability of the sail. There are a number of perturbative effects. These include laser instabilities and laser mode issues, differential forces on the sail and mechanical modes in the sail, heating of the sail and laser pointing instability.
>This is a complex sets of issues that requires a significant amount of research and development. This will not be trivial.
I believe these issues are show stopping rather than "not trivial" You can never fabricate a probe of small enough mass which has enough area for laser propulsion to work effectively whilst not tearing itself to pieces or overheating (at least not to anywhere near relativistic speeds).
A paper produced looking at the feasibility of such a system https://arxiv.org/pdf/1604.01356.pdf says
>A critical issue will be the stability of the sail. There are a number of perturbative effects. These include laser instabilities and laser mode issues, differential forces on the sail and mechanical modes in the sail, heating of the sail and laser pointing instability. >This is a complex sets of issues that requires a significant amount of research and development. This will not be trivial.
I believe these issues are show stopping rather than "not trivial" You can never fabricate a probe of small enough mass which has enough area for laser propulsion to work effectively whilst not tearing itself to pieces or overheating (at least not to anywhere near relativistic speeds).