We want to compare a laser with a normal light source approximated by a black body radiator. A 2 mW HeNe-laser with the wavelength 633 nm has a relative spectral purity (Av/v) of 10-12. We make the assumption that all the light is evenly distributed within the frequency width and over an area of 1 mm. a) Calculate the spectral emittance , (emitted intensity per frequency interval). b) What is the temperature of a black body radiator with a wavelength maximum at 633 nm? c) Calculate the spectral emittance , of a black body radiator given in b) at its maximum. The emittance is connected with the energy density by: P =Pv.