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).
The amount of safety when working with lasers is ridiculous. And for a good reason, you can get permanent eye damage faster than the blink of an eye.
Please, don't play with lasers. At all. Even supposedly "safe" lasers can output far more light than expected.
Not to mention the ones that have peaks in invisible parts of the spectrum.
Another friend’s favorite saying is, “do not look into laser with remaining eye.”