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Whatever refracts the light will have to stand up to the beam for long periods of time. Maybe it's a materials science problem.

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As long as it doesn't absorb the light, it's fine.

Just like the electric cables for your water kettle typically don't get hot.

Your kettle's power cable is sized to handle the relatively tiny current put into it, but even then it does warm up slightly. Try to run a million amps through it, and it will vaporize.

This type of laser carries so much energy that even a tiny fraction of a percent absorption will add up quickly, hence the propensity for injury.

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