Available Photonics Experiments:

P5885 Laser gyroscope PDF Download page

  • Sagnac interference
  • Helium Neon ring laser
  • Ring laser modes
  • Single mode operation
  • Fringe detection
  • Mode lock-in effect
  • High precision angle measurement
  • Examples of investigations and measurements
OX Principle of operation
The ring laser is formed by three mirrors M1, M2 and M3 and the Helium Neon laser tube. In such a configuration the laser light is travelling in two directions, clockwise (cw) and counter clockwise (ccw). At mirror M2 a small fraction of both beams is coupled out. The cw beam passes the beam splitter cube BSC and is divided by 50/50 %. The ccw beam is deflected by the mirror M4 in such a way that the ccw beam also passes the beam splitter cube BSC and that they travel collinear to each other. At the photodetector PD1 and PD2 the beat frequency of both modes are measured.
The axis of rotation is chosen in such a way that the centre of rotation lies inside the centre of the equilateral triangle formed by the three mirrors or the propagating laser beams respectively.
OX Set-up of the HeNe laser gyroscope
All three mirrors M1, M2 and M3 are mounted into high precision adjustment holder. The Helium Neon tube is placed into two XY adjustment holder enabling the centre adjustment of the tube with respect to the optical axis of the ring laser cavity. For the initial alignment a pilot laser is attached to the mirror holder of M2.
Once the ring laser is operating, the cw and ccw beams are aligned collinear to each other. The beam bending assembly is used to align the ccw beam collinear to the cw beam.
The platform carrying the ring laser is mounted on top of a stepper motor driven rotary table. The stepper motor is controlled by a driver with USB computer connection.
OX Measurements, lock-in effect
The provided software allows the control of the angular speed in degrees per second. Furthermore the rotation angle (maximum 270 degrees) and the periodicity of the swing can be set. The beat frequency is displayed by the frequency counter (4) and can also be read from the software via the USB bus of the counter.
In such a way the beat frequency is measured for a set of angular speeds. From the plot of the data the slope is taken which is related to the scale factor of the gyroscope.
It will be noticed that in a certain region around the zero point no beat frequency will occur although the table is rotating slowly. This is due to the well known lock-in effect which will be investigated in more details with smaller steps of the angular speed around the zero point.
  • P5885 HeNe Laser Gyroscope consisting of:
18X-XP161Manual HeNe laser gyroscope
2ED-00341HeNe Laser high voltage supply 6.5 mA
3ED-00801Photo diode amplifier 4 channel PDA-01
4ED-01101Fringe up and down counter FC-01 with quad input
5ED-03001Stepper motor controller, 1 Axis, USB
6LS-01801Alignment laser 532 nm with power supply
7PM-03301Fringe detection unit
8XM-05901Gyroscope base plate
9XM-06001Rotation unit
 Required Options:  
 TP-01001Oscilloscope 100 MHz digital, two channel
 TP-02101PC Pad