Could someone please explain what the limits to Quasi-CW is? ie. If I have a train of square pulses, to what limit can I make the approximation that it can be treated as a Continuous Wave signal? If that question was too vague here is my situation: In Non Linear Optics you need lots of "watts" of power, now a 50W CW laser is impractical due to many reasons...so we use pulses...the shorter the pulse the higher the peak power. However, most of Non Linear Optics theory relies on the fact that we are using CW lasers, but how short can you make a pulse until its no longer considered CW??