How many photons are in the laser pulse?

A laser pulse with wavelength 510 nm contains 4.40 mJ of energy. How many photons are in the laser pulse? (1 J = 103mJ)

Answer 1

Energy per photon = h*c / wavelength = 6.6*10^-34 * 3*10^8 / (510*10^-9) J
= 3.88*10^-19 J

No. of photons = total energy / energy per photon = 4.40*10^-3 J / 3.88*10^-19J
= 1.13 * 10^16 photons
= 11,300,000,000,000,000 photons

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