Color-and-depth-encoded illumination enabled adaptive axial resolution in volumetric measurement with particle imaging velocimetry

Rainbow particle image velocimetry (PIV) is an emerging technique that enables three-dimensional (3D), three-component (3C) flow measurements using a single camera. Although it could provide snapshot 3D imaging capability, its application in high-resolution, volumetric velocity measurements has been limited by the rigid coding format of the beam. This limitation results in an inconsistent resolution when the beam width varies with the imaging volume, making it challenging to adapt this technique to diverse experimental conditions. Here, we introduced a color-and-depth-encoded illumination PIV technique with advanced beam modulation for adaptive axial resolution in volumetric measurements. Our method enabled adaptive beam coding with electrical control of mirror arrays, where the spatial pattern of the illumination beam is adjusted by programming the mirror orientations through digital signals. This allows the coding format to adapt to varying imaging volumes without compromising the resolution. With a comprehensive calibration process, the feasibility of this method was validated by reconstructing the translational motion of particles and imaging the vortex flow field generated by the motor. The results demonstrated a reduction in the particle color recognition error and improved resolution, highlighting the potential of this technique for advanced flow measurements.