Question

a ruby laser delivers 10 ns pulse of 1 MW average power.IF all the photons of same wavelength 694.3nm how many photons are contained in the pulse?

Answer 1

Thank you for asking this question. Here is your answer:

The energy in each pulse is

E = Pt =  (1.00 × 10^6 W)(1.00 × 10^−8 s) = 1.00 × 10^−2 J

The energy of each photon is

Eγ = hf = hc /λ

= (6.626 × 10^−34 )(3.00 × 10^8 )  /  694.3 × 10^−9

J = 2.86 × 10^−19 J

N = E /Eγ

= 1.00 × 10^−2 J  / 2.86 × 10^−19 J / photon

= 3.49 × 10^16 photons

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