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Calculate the number of photons in each pulse if the pulsed laser emits photons of $\lambda$ = 900 nm with 40 mW average power per pulse & a pulse duration of 5 ns.
written 6.9 years ago by gravatar for neeta.vanage neeta.vanage • 870 modified 2.8 years ago by gravatar for pedsangini276 pedsangini276 • 4.8k

Subject :- Applied Physics 2

Topic :- Lasers

Difficulty :- Medium
engineering physics
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written 6.8 years ago by gravatar for neeta.vanage neeta.vanage • 870 modified 6.8 years ago by gravatar for saurabhsingh saurabhsingh • 40

To Find:

$n = ? \\ $

$ \lambda = 900 * 10^{-9} m \\ P = 40 * 10^{-9} W \\ t = 5 * 10^{-9} sec \\ E = P * T \\$ $$ \text {E = hv is energy of one photon }\ $$

$ \text{Therefore energy of n photons will be E = nhv}\\ $

$ \text{But v =} c/ \lambda \\ $

$ nhc/ \lambda = P * t \\ $

$ {n = P * t * (\lambda) / h * c} \\ $ $ n = 40 * 10^{-3} *5 *10^{-9} * 900 * 10^{-9} / 6.634 * 10^{-34} * 3 * 10^{8} \\ n = 9.044 * 10^{12} \\ $
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