Harmonic-Assisted Direction-Sensitive Infrared Rotational Sensing

Infrared rotation metrology is essential for both classical and quantum sensing applications. On one hand, vectorial structured light has emerged as a powerful tool to enhance sensitivity, enabling full-vectorial characterization of rotating objects through polarization-resolved fields. On the other hand, nonlinear frequency conversion provides a promising solution to the intrinsic limitations of direct infrared detection by converting infrared signals into the visible spectrum. However, integrating vectorial structured light with nonlinear frequency conversion remains challenging, as phase-matching constraints often lead to the loss of vectorial information. In this work, we introduce a harmonic-assisted approach by utilizing a rotation reference wave to enable direction-sensitive infrared detection. In our experiment, an infrared light source at 1550 nm serves as the signal to probe rotating particles, while a vectorial optical field at 1064 nm is prepared as the pump beam. These two beams are collinearly mixed in a BBO crystal via type-I phase matching, generating a visible SFG wave. Our experimental results demonstrate the ability to resolve both the angular velocity and direction of infrared rotating particles using silicon-based visible-light detectors. This method provides a robust platform for advanced infrared motion sensing and monitoring applications.