Scientists in a spin over Doppler Shift discovery

Scientists at the Universities of Glasgow and Strathclyde have discovered rotational speed can be determined by measuring Doppler Shift - the same effect utilised in radar speed guns. Doppler Shift is a phenomenon everyone is aware of, if perhaps not by name, and is most often experienced by the sound of a siren from a police car or ambulance rising and falling in pitch as it passes by. It is a result of the frequency change due to the position of the observer relative to the source, so each sound wave from an approaching siren is generated a little closer to the observer each time and a little further away as it travels away. The effect is utilised in radar speed guns, when the waves generated by the gun reflect off a car, the change in frequency is detected and speed calculated. Both of these examples concern linear motion - objects travelling along a straight path - but scientists at the University of Glasgow have discovered Doppler Shift can be used to detect rotational motion too, but only when using 'twisted light'. Researchers in the School of Physics & Astronomy used a beam of light that had 'angular momentum' - or spin - and pointed it at rotating objects. Even though the light hit the object head-on, because the light was twisted like a corkscrew, it was actually hitting the object at a slight angle.