The lasers used in the lunar ranging experiments are pulsed, in much the same way radar is pulsed, so even though the laser's peak power is very high, the avera

The lasers used in the lunar ranging experiments are pulsed, in much the same way radar is pulsed, so even though the laser's peak power is very high, the average power could be less than a watt and accomplish the desired objective. The other thing about this experiment is that it relies on autocorrelation to avoid a need for very much power. Autocorrelation depends on knowing the departure times of the outgoing laser energy and accumulating many samples at the expected return time, which is predictably and reliably related to the transmission time. This integration technique produces a clear return signal that would be lost in noise if only one sample were collected. http://en.wikipedia.org/wiki/Autocorrelation http://en.wikipedia.org/wiki/Autocorrelation In principle, if someone was patient and had good enough equipment, one could detect the reflection of a very small outgoing power level by collecting hundreds or thousands of samples. Autocorrelation is an amazing technique.