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21 March, 15:27

How many photons are produced in a laser pulse of 0.862 J at 691 nm?

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  1. 21 March, 15:47
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    To calculate how many photons are in a certain amount of energy (joules) we need to know how much energy is in one photon.

    Start by using two equations:

    Energy of a photon = Frequency * Planck's constant (6.626 * 10^ (-34) J-s)

    Speed of light (constant 3 * 10^8 m/s) = Frequency * Wavelength

    Which means:

    frequency = Speed of Light / Wavelength

    So energy of a photon = (Speed of light * Planck's constant) / (Wavelength)

    You may have seen this equation as E = hc / λ

    We have a wavelength of 691 nm or 691 * 10^-9 meters

    So we can plug in all of our knowns:

    E = (6.626 * 10^ (-34) J-s) * (3.00 * 10^8 m/s) / (691 * 10^-9 m) =

    2.88 * 10^ (-19) joules per photon

    Now we have joules per photon, and the total number of joules (0.862 joules)

    , so divide joules by joules per photon, and we have the number of photons:

    0.862 J / (2.88 * 10^ (-19) J/photon) = 3.00 * 10^18 photons.
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