My friend in college did an internship on high frequency, short pulse beams (I wanna say violet and picosecond? Which I still think was exotic at the time).

Most of his work was dealing with and accounting for reflections that left the machine. If you have a prism that’s sending 95% of the light where you want it to go, when it’s a multi watt laser you can’t just let that 5% go wherever it wants. You will blind someone. So his job was getting black bodies in all the right spots to absorb the lost light.

His safety goggles looked like even more expensive Oakleys of that era and they were (much more expensive).