Question

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?

Answer 1

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

it will be same as the power of source

$P = 3 mW$

now the energy released by one photon is given as

$E = \frac{hc}{\lambda}$

$E = \frac{6.6* 10^{-34}* 3 * 10^8}{760 * 10^{-9}}$

$E = 2.6 * 10^{-19} J$

now let say N photons per second released

$N * 2.6 * 10^{-19} = 3 * 10^{-3}$

$N = 1.15* 10^{16} per\: second$