The most common long range rangefinders use nanosecond timers to measure the delay between a pulse and a response. At 100 meters, a laser beam will take 666ns to bounce off a target, 200 meters will take 1300ns etc... The precision of this method is a lot less because of confounding factors like the precision of your timing device, refraction, etc... Data will be encoded into the laser pulses similar to a GPS signal to reduce issues with cross talk between rangefinders and jamming. These measurements are confounded by the huge speed of light. A 1 nanosecond mis-timing will result in 0.3 meters loss of precision.
A triangulating range finder (Usually a LIDAR) will further refine the above measurement by positioning sensors a distance apart to make medium distance sensing more accurate. This allows LIDAR scanners to increase their precision down into the millimeter range.