Performance evaluation of fast, high precision laser rangefinder electronics with a pulsed laser

A laser rangefinder system based on a pulsed time of flight distance measurement technique was constructed and tested. The system is composed of a receiver channel connected to a leading edge timing discriminator and time interval measurement electronics. The receiver channel consists of a wide bandwidth InGaAs photodiode with a typical rise time of 35 ps. A timing discriminator has 8 GHz equivalent input rise time bandwidth and a programmable threshold. It is capable of processing electrical pulses as short as 80 ps and is constructed using commercially available components. The time interval measurement electronics is highly programmable system. The measurement method is based on an interpolation principle where the time interval is roughly digitized by a coarse counter driven by a high stability reference clocks and the fractions between the clock periods are measured by two time-to-digital converter chips. The system has two reference clock inputs and two independent channels for measuring start and stop events. Only one 40 MHz reference is required for the measurement. The system can achieve a timing resolution better than 15 ps rms with up to 90 kHz repetition rate. The measurement range is from 0 ps up to 1 second. The performance of the system was evaluated at short distances with a pulsed laboratory constructed laser. It is a mode-locked Nd:YAG laser generating 20 ps output pulses at the wavelength of 1064 nm with a repetition rate up to 100 Hz. The system is capable of measuring distances down to 0 m. The overall measurement accuracy is estimated to be 5 mm and will be verified by the experiment.