A helium-neon laser that has a power rating of \(0.250 \mathrm{~mW}\) operates at a wavelength of \(633 \mathrm{~nm}\) and a beam diameter of \(2.00 \mathrm{~mm}\). Calculate \((a)\) the energy per photon, (b) the number of photons emitted per second, (c) the momentum per photon, and \((d)\) the pressure exerted on an absorber on which the beam is incident.