The red laser beam operating at a wavelength lambda = 630 nm. It has the form of a cone with an angle of divergence of 10 ^ -4 rad. The radiated laser power Po = ZmVt. At what maximum distance L observer can see the laser light when the eye reliably detects 100 photons per second. Pupil diameter d = 0,5 cm. The absorption of light is not taken into account. The beam diameter at the laser output is much less than d.

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