Is there anyone who has experience in setting up optical system for exciting a sample using Q-switch mode of Nd:YAG laser? I am currently looking at the optical system which I did not setup (someone else did, but the person is absent and cannot contact). I have no background whatsoever in optical system setups, and I have a problem that the laser is emitting red light for some reason. I am currently trying to use THG of 1064 nm emission from Nd:YAG (355 nm). However, I do not know the diagnostics of this optical system when it's not working right. What can be wrong? Could it be the non-linear optical crystal?