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 x 10(-30) (2.7 arcsec), respectively. The linearity of the sensor response has been verified over a range of 1 m and +/- 0.4 degrees. Using three retrorefiector 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.