An argon ion laser puts out 5.1 W of continuous power at a wavelength of 532 nm. The diameter of the laser beam is 5.8 mm .

If the laser is pointed toward a pinhole with a diameter of 1.2 mm, how many photons will travel through the pinhole per second? Assume that the light intensity is equally distributed throughout the entire cross-sectional area of the beam. (1 W = 1 J/s).

Hint: Use the formula for the area of a circle (A = πr^{2}) to find the cross-sectional area of the beam and of the pinhole and determine what fraction of the power gets through the pinhole.

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