If = 533, what is the minimum diameter of the circular opening from which the laser beam emerges? The earth-moon distance is 3.84×105.
Scientists use laser range-finding to measure the distance to the moon with great accuracy. A brief laser pulse is fired at the moon, then the time interval is measured until the "echo" is seen by a telescope. A laser beam spreads out as it travels because it diffracts through a circular exit as it leaves the laser. In order for the reflected light to be bright enough to detect, the laser spot on the moon must be no more than 1 in diameter. Staying within this diameter is accomplished by using a special large-diameter laser.