Hi! I am currently self-learning laser right now, and I have some questions about it.. 1. We know that water moves from higher to lower altitude, air moves from higher to lower pressure, electrons move from higher to lower potential. What about photons? Where would it go? 2. Why would only certain discrete frequencies/wavelengths are allowed in a laser cavity? Any analogy? 3. I still can't understand how would many modes can exist in a laser at the same time. Any analogy? 4. How exactly AM modulator (in laser mode-locking) works? The thing that i can't digest is that if you have, say, an electric signal of phase ^v (please it's a full cycle sin function) which goes to the modulator, and and at the same time other modes which is a \/ (cos function), and both enter a modulator, and also other modes like just ^ or v (half cycle..is it even possible?), how and what the modulator does to make all the output are the same ^v ? How can the modulator is so smart to know when to shape what, what to shape what, and how to shape what? I mean, the electric signal of the modulator is fixed, right? *I think its math is the most complicated functions i have ever seen..:( Thank you for the answer! I actually still have many but i am afraid nobody answers if it is too many..