Ultra-thin f-theta metalens with high focus resolution and large field of view

Conventional f-theta(f-θ) lens systems often rely on cascading multiple lenses or adopting complex surface profiles to achieve high-precision scanning and laser processing over a large field of view (FOV), leading to significant increases in system volume and manufacturing complexity. This study presents an ultra-thin f-θ lens for a 10.6µm laser processing system, realizing high-performance scanning through a collaborative optimization method of cascaded metasurfaces. Simulation results based on dual-layer cascaded metasurfaces show that within the ±32° light deflection range, the spot diameter remains below 20µm, the maximum f-θ distortion is controlled at 0.19%, and the Strehl ratio (SR) across the entire FOV exceeds 0.99, verifying the system's imaging performance approaching the diffraction limit. Phase sampling analysis of the cascaded metalenses indicates that when the sampling step varies within 3-9µm, there is no significant difference in spot performance, which greatly reduces the fabrication difficulty and cost. Further research demonstrates that when the phase mutation rate is controlled within 8%, the system maintains stable scanning characteristics, while exceeding 9% leads to severe wavefront distortion and drastic deterioration of optical performance, providing a quantitative basis for processing error control. The wavelength analysis of the designed f-θ lens reveals that it maintains good performance within an 80 nm bandwidth. This study provides an integrated solution for compact laser processing systems, and its technical achievements can promote the large-scale application of metasurface optical elements in optical imaging, optical metrology, and laser processing.