OAM-assisted rotational Doppler velocimetry at 1.5 μm wavelength through atmospheric turbulence

Rotational Doppler effect has been recognized as a pivotal enabler to develop rotational Doppler LiDAR. Current rotational Doppler velocimetry schemes focus mainly on free-space detection. While several turbulence-related studies have been developed, their laser’s wavelength is restricted within visible light ranges. Here, we study rotational Doppler detection at eye-safe communication band, which can be conducive to passing through atmospheric turbulence, due to the operation at atmospheric window. Firstly, we measure the orbital-angular-momentum (OAM) light modes at 1.5 μm wavelength. And then, we emit such modes onto a rough rotator surface with random postures versus light source. Subsequently, we measure the rotational Doppler spectrum under alignment and misalignment conditions, where frequency-shifted intervals can be used to determine rotational velocity magnitude. Finally, we evaluate the rotational velocimetry performance by analyzing relative measurement error. Our findings indicate OAM-assisted rotational Doppler velocimetry can be expanded to communication band when meeting atmospheric turbulence, which may be used to long-range weather sensing, celestial observation and beyond.