One can use transparent (to neutrons) aluminum (remember one of the Star Trek movies) grazing incidence final mirrors (GIMM) - neutrons go through (transparent Al substrate) and laser light reflects.

For a practical fusion energy system one needs the product of electrical efficiency of the plasma heating device (neutral beams for tokamaks and the laser system for laser IFE) and the fusion gain to be greater than about ten -- so that most of the electrical power goes to the grid rather than powering the systems that support the fusion power plant. Per the paper the 16% intrinsic efficiency of the ArF laser could allow 10% "wallplug" electrical efficiency -- so one needs gains (ratio of fusion energy out to laser energy in) to be at least 100. The 1D and 2D simulations in the NRL Phil. Trans A paper indicate that with the ArF laser the gains needed for IFE (>100) could be achieved with less laser energy than already achieved on NIF.

All truly innovative approaches to fusion are presently funded by the private sector -- e.g. MIT-Commonwealth Fusion Systems high field tokamak (smaller lower cost) -- and the General Fusion imploding liner approach -- which is based on the NRL LINUS concept from 30 years ago. The folks @ NRL may follow that route with a first of its kind path to lower cost laser IFE.