Available Photonics Experiments:

P5882 Laser Range Finder PDF Download page

  • Short pulse laser diode
  • Laser energy
  • Peak pulse power
  • Beam collimation
  • Si PIN Photo Detector
  • Light Echoes
  • Time of Flight
Principle of operation
The emission of a pulsed laser diode is collimated and aimed to the target for which the distance shall be determined. The short laser pulse (100 ns) travels with the speed of light and hits the target. The scattered light is detected by the Si-PIN photodiode after passing the receiver lens. Based on the time of flight and the known speed of light the distance to the target is calculated.
  • Examples of investigations and measurements
Measuring time of flight t
The laser diode is mounted in a 4 axis adjustment holder (4). The divergent emission of the laser diode is collimated by means of the optics accommodated into the mounting plate (7). The electronic device (2) provides the trigger pulses and power for the laser diode. The device is fully controlled by a microprocessor and a clear display informs about the values. The control and settings of the parameters is done by a one knob control. The peak power is set by the discharge voltage and the average power is controlled by the repetition rate of the trigger pulses.
The scattered light is collected by the receiver lens (8) and imaged to the SiPIN photodetector. The amplifier is built into the same housing as the photodiode to achieve highest sensitivity and fast response. Via the coaxial cable terminated with a BNC connector the amplified signal can be connected to an oscilloscope. In the same way the trigger pulse of the laser diode is used to trigger the oscilloscope. This arrangement allows the determination of the time of flight by means of the oscilloscope

Measuring the speed of light c
If the distance ds to a target is known the speed of light can be measured in this way. The distance should be chosen in such a way that a significant delay between the trigger and echoed pulse is obtained.

Characterising the laser pulse
A laser pulse is characterised by its:

    Peak power
    Rise time
    Pulse energy in Joule

These parameters are determined by means of the oscilloscope. In contrast to continuous operating lasers where the output power is given in W, here the energy per pulse is given in Ws or Joule.
  • P5882 Laser Range Finder consisting of:
Item Code Qty Description
1 3L-0360 1 BNC connection leads, set of 2
2 ED-0090 1 Pulsed laser diode controller PLDC-01
3 ED-0310 1 Photodetector, ultrafast with amplifier
4 LS-1300 1 Pulsed diode laser module
5 MC-0250 2 Profile Rail MG-65, 300 mm
6 PM-0070 1 Infrared display card, spectral range 0.8 -1.6 µm
7 XM-0030 1 Module B - Collimating optics on carrier MG-65
8 XM-0040 1 Module F - Focussing optics, f=60 mm
Required Option:
  TP-0100 1 Oscilloscope 100 MHz digital, two channel