Acousto-Optic Deflector Focusing System for 3D Scanning

The patent replaces mechanical scanning mirrors with acousto-optic deflectors (AODs) that use acoustic waves to deflect and focus the laser beam. This substitution eliminates mechanical moving parts in the scanning path, enabling scan rates exceeding 1000 Hz while maintaining precise 3D positioning capability. The AODs control beam direction and focus through acoustic frequency modulation rather than physical mirror movement.

The patent implements dynamic focus adjustment by varying the acoustic frequency sweep rate in the AODs. By changing the sweep rate, the system can dynamically adjust the focus position along the optical axis (Z-axis) while simultaneously performing lateral scanning in the XY plane. This dynamic control enables rapid 3D volume scanning without mechanical movement of the objective or sample stage.

The patent applies different acoustic frequency sweep rates to different AODs based on their specific functions. The first AOD (for X-axis scanning) uses a higher sweep rate optimized for lateral scanning speed, while the second AOD (for Z-axis focusing) uses a lower sweep rate optimized for precise focus control. This localized optimization of sweep rates for each component's specific role minimizes spatial and temporal dispersion while maintaining overall scanning productivity.

The patent introduces a telecentric lens system as an intermediary between the AODs and the sample. This optical intermediary compensates for the spatial and temporal dispersion introduced by the AODs, particularly for ultra-short laser pulses used in multi-photon excitation. The telecentric lens system recollimates the divergent beam and maintains pulse duration uniformity across the scanning field, thereby preserving temporal resolution.

The patent removes the half-wave plate component from the optical path entirely. Instead of using a half-wave plate to rotate polarization between AODs, the system directly uses the polarization state output from the first AOD as input to the second AOD. This extraction of the problematic optical element eliminates the associated material dispersion and bandwidth reduction while maintaining the ability to operate with extraordinary polarized light for maximum bandwidth.

The patent changes the acoustic frequency parameters of the AODs to compensate for polarization effects. By carefully controlling the acoustic frequency sweep rates and center frequencies of the AODs, the system maintains optimal diffraction efficiency and minimizes spatial dispersion without requiring polarization rotation. This parameter optimization allows direct coupling between AODs with different polarization states, avoiding the need for half-wave plates.