Q) Why is it easy to see the output of a laser pointer on a screen illuminated by an overhead projector. Assume 1mW laser and 500W quartz halogen bulb. Explain quantitatively, and state all other assumptions. Im not sure whether it involves the coherence length/time of the two waves, visibility or some variation of the two. Im really desperate for help on this one. Im gonna ask a double question (still lasers though) since this is my first post Q) second things is simply what controls whether a energy level scheme is suitable or unsuitable for CW operation I believe it depends on the difference between the two decy rates, or is that slightly wrong? or totally?