Structured light has profoundly advanced optical manipulation, processing and imaging. However, its practical deployment in free space is limited by the constrained solutions of Helmholtz equation, which are bound to fixed propagation laws. Here, we reframe structured light as optical flows through a hydrodynamic description beyond the conventional field formalism, achieving flexible light structuring in free space via streamline engineering. Within this framework, we demonstrate the on-demand generation of diverse families of beams, with tailored propagation dynamics, including Gaussian, Bessel, Airy and vortex beams, and introduce specialized modes that overcome complex propagation challenges. To validate the designed energy streamlines, we perform optical tweezers experiments, treated as analogous to fluid particle-tracking velocimetry, demonstrating potential for high-precision optofluidic manipulation. For free-space optical communication, we show how vortex modes with a tailored flow can improve channel capacity, resilience to turbulence and non-line-of-sight capability. The hydrodynamic framework reported here provides precise control over light in free space, opening avenues in optomechanics, optofluidics, imaging, metrology, and communications.
Yan et al. (Wed,) studied this question.