A Compact Three Degrees-of-Freedom Motion Sensor Based on the Laser-Self-Mixing Effect

The simultaneous measurement of the linear displacement and two rotation angles (yaw and pitch) of a moving object using a laser sensor based on the self-mixing effect is reported. The laser head includes three commercial diode lasers equipped with monitor photodiodes. The target is a plane mirror attached to the moving object. The linear and angular resolutions are 0.7 $\mu$m and $0.8\times 10^{-3\circ}$ (2.7 arcsec), respectively. The linearity of the sensor response has been verified over a range of 1 m and $\pm$0.4$^{\circ}$. Using three retroreflector prisms with a diameter of 10 mm instead of the plane mirror, the angular range of yaw and pitch has been improved by one order of magnitude.