Scientists use later range-finding to measure the distance to the moon with great accuracy. A brief lazer 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 mon must be no more than 1.0 km in diameter. Staying within this diameter is accomplished by using a special large diameter laser. If λ=532 nm, what is the minimum diameter of the circular opening from which the laser beam emerges? The earth-moon distance is 384,000 km.