In a laser range-finding experiment, a pulse of laser light is fired toward an array of reflecting mirrors left on the moon by Apollo astronauts. By measuring the time it takes for the pulse to travel to the moon, reflect off the mirrors, and return to earth, scientists can measure the distance to the moon to an accuracy of a few centimeters. The light pulses are \(100 \mathrm{ps}\) long, and the laser wavelength is \(532 \mathrm{~nm}\). When the pulse reaches the moon, it has an intensity of \(300 \mathrm{~W} / \mathrm{m}^{2}\). How many photons strike a single 4.0-cm-diameter mirror from one laser pulse?