Maybe the endgame is to create a partially open subway station with a similarly concave design at the opposite site of the focus and then put a NdCrYAG crystal

Maybe the endgame is to create a partially open subway station with a similarly concave design at the opposite site of the focus and then put a NdCrYAG crystal there... [0] [0] https://en.wikipedia.org/wiki/Solar-pumped_laser https://en.wikipedia.org/wiki/Solar-pumped_laser