LM-0400 Laser Range Finder

Laser range finding is one of the applications of light detection and ranging known as LIDAR. The principle of this technique is well known from the RADAR (Radio wave Detection And Ranging). Instead of using radio waves, the LIDAR uses light as electromagnetic wave. Both techniques are based on the emission of a short pulse of electromagnetic radiation and the reception of back scattered signals from a target. The time t between the emission and reception of the pulse is measured and the distance d is calculated based on the velocity v of electromagnetic radiation. Using v≈3×108 m/sec for the speed of light, the time interval t for a distance d of 10 m will be 60 ns.
The pulse duration must be modified to match the required resolution and distance. In this experiment the shortest pulse duration is 50 ns with a rise time of 5 ns. When the laser pulse is launched the receiver photo detector is also used to generate a start pulse signal which serves as trigger for the oscilloscope. The peak power of the laser diode amounts to 70 W within 100 ns which is related to an energy of 4µJ only. The intensity of the back scattered is very low compared to the laser pulse it self depending the scatter efficiency of the target. Furthermore the intensity drops with 1/r² where is the distance to the target. Consequently a photodetector with amplifier is applied. The controller allows also the characterization of the laser diode itself. The output power and pulse width as function of the parameters like charge voltage and discharge time can be measured and optimized for the length to be measured.