Laser Range finder with TOF method

[Sobakava]

I would like to know how commercial laser rangefinders with time of flight method measures so short (picoseconds) delays between signal of the detector front of the laser and detector gets reflected lights from object?

I saw something called timing discriminator...
Does anyone info on pratical design of tof rangefinders?

regards

 

[flatulent]

They modulate the amplitude with a sine wave and then use a phase detector on the received signal. With a high SNR and long integrating time a fraction of a degree can be measured.

First they use a low frequency modulation to get the approximate range. This is low enough to go through less than one cycle of phase shift for the maximum range of the system.

Then they use a high frequency signal with many cycles in the maximum range. This phase measurement gives several possible ranges which are compared with the one from the low frequency to select the right one.

 

[Sobakava]

for measuring distances 20cm to 1m, what should be the usable modulation frequency?