Now instead a 3-mw laser of wavelength λ = 760 nm is directed into the interferometer (with the mirror m1 at the displacement calculated in part a). how much power is detected at d1?

power received will always remain same and does not depends on the distance

it will be same as the power of source

now the energy released by one photon is given as

now let say N photons per second released

current flows in a wire

f=ma newton

f=100x2.5=250n