The lunar ranging station at the University of Texas McDonald Observatory has made more than 1800 range measurements to the four lunar retroreflectors during the first six years of its operation. Each range consists of a normal point constructed of from 5 to 20 single photoelectron returns. Normal point accuracies to about 4 parts in 1010 (± 10 cms) have become routine. The availability of excellent commercial timing equipment, similar to that used for nuclear time-of-flight experiments, means that the error budget for such a measurement is primarily dependent on the width of the transmitted laser pulse (currently 3 nanoseconds FWHM). Second generation systems using mode-locked, subnanosTRond lasers can probably achieve routine normal point accuracies approaching one part in 10 (± 2 cms). High speed pockel cells, capable of slicing sharp edges on relatively long laser pulses, may permit such accuracies to also be realized with conventional Q-switched lasers.
Eric C. Silverberg,
"High-Accuracy Range Measurements To The Moon", Proc. SPIE 0094, High Speed Optical Techniques: Developments and Applications, (18 January 1977); doi: 10.1117/12.955142; https://doi.org/10.1117/12.955142