Synthesis and Dynamic Control of Acousto‐Optic Multifocal Extended‐Depth‐of‐Focus Beams Based on the Superposition of Multi‐Chirp Signals

Abstract

Long depth‐of‐focus (DOF) beams maintain stable focusing over an extended axial range and are important for advanced microscopy, volumetric imaging, optical manipulation, and laser processing, particularly high‐aspect‐ratio glass micro‐hole drilling. Conventional methods typically rely on static or mechanical optical control, limiting high‐speed adjustment of the DOF, focal position, and axial intensity distribution. Acousto‐optic deflectors (AODs) provide an inertia‐free, high‐speed, and programmable platform for dynamic axial optical field control. By applying multi‐chirp signal superposition to a pair of orthogonally arranged AODs, acoustically induced gratings can be synthesized to achieve dynamic control of multifocal extended‐DOF beams. However, the superposition of multiple axially focused sub‐beams with different frequencies produces a beat effect, causing periodic fluctuations in the intensity and spot morphology of the composite optical field and thus affecting its stable generation. To address this issue, phase locking is combined with temporal synchronization between the laser pulses and acoustic field to suppress the adverse influence of the beat effect on the composite optical field. Experimentally, a 40.0 mm effective DOF with a 73.4 µm spot radius is achieved, along with dynamic control of axial focal position and intensity distribution. This method provides a high‐speed, programmable approach for dynamic axial optical field control.