I've heard that common way to get 354nm laser is to triple 1064nm Nd:YAG one.
But how to make non-linear crystal to do tripling instead of doubling? What are the best crystals for tripling and what's the efficiency?
You typically use a frequency doubler (more efficent) and then mix the doubled and original in a second crystal to generate the tripled as a harmonic (see http://www.rp-photonics.com/frequency_tripling.html)
No idea how that happens - personally I always considered them to be magic crystals !