I posted a question about Rabi frequency here https://www.physicsforums.com/threads/what-is-rabi-frequency.331082/ some times ago. The replies there answer some of my questions but I am still looking for detail explanation on the relation between Rabi frequency and the power of the beam. I read some more materials online. There I understand that if I have a 2 level system where the Rabi frequency is a constant if the input laser is of constant power. I am thinking if we shine that laser beam (as pulse with duration ##\Delta t##) to the system. How can we figure out the power of the laser if we know Rabi frequency ? I am thinking ##\hbar \Omega## is of the unit of energy so is the power of laser should be ##\hbar\Omega/\Delta t## if ##\Delta t## is the duration of the pulse? Someone said this is not correct because if depends on how much the frequency of laser off from the resonance frequency also. But how do we add that and get the correct expression for power?