A ruby laser emits light at wavelength 694.4 nm. A laser pulse is emitted for 12.0 ps and the energy release per pulse is 150 mJ. (a) We have to find the length of the pulse, and (b) the number of photons contained in each pulse.

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Energy of a photon of wavelength will be

(a)

As the laser pulse is emitted for 12.0 ps, the length of the pulse will be

(b)

As the energy release per pulse is 150 mJ, the number of photons of energy contained in each pulse will be