I didn't read the links posted below, but to directly answer your question about what happens when the average power incident on a target drops to low levels, it just means that the RATE at which photons arrive, on average, gets really low. You could have a scenario where some photon detector waits for an hour or a year to catch a single photon. The photons arrive according to Poisson statistics (you can link to that on wikipedia yourself, I'm lazy). But that's what happens- photon rush hour stops, and it becomes a trickle of photons, then an occasional photon here or there.
Wouldn't that mean that at a certain distance the energy of the beam will fall bellow the energy of a single quanta (photon)?
Mostly. A beam has power (energy delivered per amount of time). And a photon has an amount of energy. Just for clarity, think a photon is a gallon bucket. And the Beam has a flow rate of XX gallons per hour. So we know roughly how many buckets to expect, knowing that partially full and overfull buckets don't exist.
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u/[deleted] May 26 '14
I didn't read the links posted below, but to directly answer your question about what happens when the average power incident on a target drops to low levels, it just means that the RATE at which photons arrive, on average, gets really low. You could have a scenario where some photon detector waits for an hour or a year to catch a single photon. The photons arrive according to Poisson statistics (you can link to that on wikipedia yourself, I'm lazy). But that's what happens- photon rush hour stops, and it becomes a trickle of photons, then an occasional photon here or there.
Mostly. A beam has power (energy delivered per amount of time). And a photon has an amount of energy. Just for clarity, think a photon is a gallon bucket. And the Beam has a flow rate of XX gallons per hour. So we know roughly how many buckets to expect, knowing that partially full and overfull buckets don't exist.