題組內容

6. A 20-mW helium-neon laser (λ = 632.8 nm) emits a beam of circular cross-section whose diameter is 1 mm. Assume the beam has a uniform intensity over its cross section. (a) Find the energy of one photon for this laser in unit of eV: (17)______ (b) Find the Poynting vector of this laser beam. (18)______ (c) What is the intensity of this laser beam? (19)______ (d) What total momentum per unit length of the beam is carried? (20)______

18.