Correct, your limitation would be the SHG. In a real world about 500MW/cm2 is about the limit. Understanding that EVERYTHING must be PERFECT. to obtain 200 W of green. system would probably have to be assembled in a clean room free from contaminates, hermetically sealed. It is a bit out of the realm for most of even the best engineers. Im not saying it cant be done (around 100w of green is routine these days) but it is not an easy task.