Forgot to add this, no macroscopic object launched from earth has ever achieved even a fraction of this speed.
I hate Crap Science. Some fools read this crap science and believe it.
The energy required to accelerate just a few grams to these velocities is beyond our ability. We are talking megatons of energy over a few seconds. That is one hell of laser and I do not want to be 1000 miles from it when they pull the trigger. The sail would need to 100 percent reflective as just a minuscule percentage of the energy not reflected would instantaneously render it plasma and perhaps atomic particles.
I hate Crap Science being published as science. Those that do are not persons of science.