The pulses are separated by the time it takes light to make a round trip between the laser mirrors.
From the newscientist.com
The laser rangefinder finds the distance of a surface by timing the round-trip time of a pulse of light.
From the en.wikipedia.org
He refined Foucault's methods in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt.
From the en.wikipedia.org
These pulses will repeat at the round trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator.
From the en.wikipedia.org
The round trip light travel time of more than two seconds is apparent in all the real-time recordings of the lunar audio, but this does not always appear as expected.
From the en.wikipedia.org
Since the speed of lightc is known, the round-trip time determines the travel distance of the light, which is twice the distance between the scanner and the surface.
From the en.wikipedia.org
Due to the high speed of light, timing the round-trip time is difficult and the accuracy of the distance measurement is relatively low, on the order of millimeters.