Generalized Doppler effect for high-accuracy frequency shift measurement

Laser Doppler effect enables a wide range of precision measurements. However, its traditional implementations, including linear, rotational, and vectorial forms, have historically been treated as isolated phenomena, and meanwhile, their accuracy is fundamentally limited by the achievable frequency shift magnitude due to single controllable parameter. Here, we report a generalized Doppler effect that overcomes these limitations and enhances metrological accuracy. Such effect arises when tailored vectorially polarized dual-vortex fields derived from spin-orbit coupling interact with moving scatterers. In doing so, we observe four simultaneous spectral signatures in a single measurement, including conventional Doppler signal (DS), Doppler polarization signal (DPS), and two novel Doppler polarization-vortex signals (DPVSs). Crucially, the advanced DPVSs with coupled polarization (m) and orbital angular momentum (ℓ), produce amplified frequency shifts that enhance relative measurement accuracy by factors scaling as κ₁(1 + |m|/ℓ) and κ₂(1 + ℓ/|m|), compared with conventional DS and DPS schemes. Furthermore, directional ambiguity inherent to these shifts can be resolved via phase analysis of either initial polarization offset or analyzer angle difference. Our generalized framework not merely unifies previous Doppler formulations but offers a potential pathway to substantially improved Doppler metrology, enabling unprecedented accuracy in high-resolution fluid vorticity mapping, quantitative hemodynamic monitoring, and next-generation LiDAR systems.