I do not know how to do the second part of this question. I never learned this. A laser used to weld detached retinas puts out pulses of 640 nm light, 25 ms long, which average 0.50 W output during a pulse. i) how much energy can be deposited pre pulse? ii) If the energy of a light particle (photon) is about 3 * 10^-19 J, how many photons does each pulse contain? I do not know how to get this.