First calculate your gains and losses intracavity. The KTP crystal sucks power out of the system, it is a loss, for example. Then start playing with optics.
Most designers of simple lasers try to make the pump spot size smaller then or equal to the desired mode volume of the laser.
So if you want a 0.5 mm Green beam, you would aim for a 0.4 mm 808 nm spot size that has a long volume in the rod.
Then the thermal lensing comes into play, and that is where you need the modeling software.
If the laser was pulsed where the 55% green conversion is obtainable, you know you have a 55% loss intra-cavity that you know you need to overcome. In reality KTP in CW is probably going to be ~25-30%.
Siflvast's book covers estimating your gains and losses, and I know you have a copy.
Barkhousen's criteria for oscillation has to be met, which says gains must exceed total losses and you need positive feedback phase shift.
I need to set up a FTP some how so you can have access to some YAG design PDfs. I cant post them publically, due to copyright.
Steve
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...