The rotational Doppler effect (RDE), where the frequency shift is proportional to both the orbital angular momentum $\ell$ of light and the rotational speed of the object ($\mathrm{\Delta }f\propto \ell \mathrm{\Omega }$), has proven to be a powerful tool for rotational speed sensing and measurement. However, the current detection technique is mainly based on coherent laser sources. There is scarce mention of using partially coherent light sources, let alone sunlight. We found that under conditions of limited spatial coherence and low light—where background noise exceeds the signal—superimposing multiwavelength rotational Doppler signals significantly boosts both signal strength and signal-to-noise ratio, enabling precise measurement of the object’s rotational speed. Our research not only furnishes a framework for exploring how light spatial coherence affects the RDE but also validates sunlight-enabled RDE detection experimentally, highlighting its potential for passive remote sensing.

Close

PrevNext

View figure in article

• Angular momentum of light
• Imaging & optical processing
• Metrology
• Optical coherence
• Rotation sensing
• Structured light