How many photons are produced in a laser pulse of 0.497 J at 469 nm?

E=hν where E is the energy of a single photon, and ν is the frequency of a single photon. We recall that a photon traveling at the speed of light c and a frequency ν will have a wavelength λ given by λ = cν λ will have an energy given by E = hc λ λ=657 nm. This will be E = (6.626 * 10 - 34) (2.998 * 108) (657 * 10 - 9) = 3.0235 * 10 - 19 J So we now know the energy of one photon of wavelength 657 nm. To find out how many photons are in a laser pulse of 0.363 Joules, we simply divide the pulse energy by the photon energy or N = E pulse E photon = 0.363 3.0235 * 10 - 19 = 1.2 * 1018 So there would be 1.2 * 1018 photons of wavelength 657 nm in a pulse of laser light of energy 0.363 Joules.