Off-axis angular velocity detection with incoherent light

The rotational Doppler effect has garnered considerable attention due to its potential to advance velocity detection technologies. Previous studies have primarily focused on measurement techniques using sources with modulated amplitude, phase, and polarization. However, a major limitation of these approaches lies in their dependence on precise alignment between the optical axis and the object's rotation axis. To address this challenge, we propose an angular velocity detection scheme utilizing incoherent illumination, which effectively accommodates off-axis deviations. Key to this success is the use of a post-modulation module, which can be easily integrated as an extension to a camera. A proof-of-principle experiment was conducted using various incoherent light sources, such as LED, demonstrating the ability to measure angular velocity under arbitrary alignment conditions. The proposed method holds significant potential for applications in velocity metrology and micromanipulation.