1. The problem statement, all variables and given/known data It's not in fact a question of homework but something I have been wondering but cannot get answers about the requirements for an observable pattern in young's experiment: 1. Polarisation: In my study, the book derived the intensity function of light assuming the light beams are polarised. But I wonder if the experiment will work if unpolarised light beam is used, or the light beams have different degree of polarisation exiting the two slits? 2. Coherence: Some information from the internet tells that "coherence" of light beam from the two slits are not actually important. But its the "spatial coherence" and "temporal coherence" that matter. I am confused by what these terms mean and cannot understand anything by referring the wikipedia. 3. Laser: Why is laser used mostly in the experiment? I understand that it is "more monochromatic" than the other light. (although I don't why) But besides that, what else matter? 2. Relevant equations 3. The attempt at a solution That's all the requirements I can think of for the young's experiment. I tried to answer the above questions but I failed. Please help! Thanks!