Reduction of spherical and chromatic aberration in axial-scanning optical systems with tunable lenses

Optical systems with integrated tunable lenses allow for rapid axial-scanning without mechanical translation of the components. However, changing the power of the tunable lens typically upsets aberration balancing across the system, introducing spherical and chromatic aberrations that limit the usable axial range. This study develops an analytical approximation for the tuning-induced spherical and axial chromatic aberration of a general optical system containing a tunable lens element. The resulting model indicates that systems can be simultaneously corrected for both tuning-induced spherical and chromatic aberrations by controlling the lateral magnification, coma, and pupil lateral color prior to the tunable surface. These insights are then used to design a realizable axial-scanning microscope system with a high numerical aperture and diffraction-limited performance over a wide field of view and deep axial range. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Biomedical research has been transformed by 3D optical microscopy techniques, including confocal [1,2], two-photon [3], and light-sheet microscopy [4,5]. In most circumstances, 3D information is obtained by capturing a sequence of images in the xy-plane while translating the optical system along the z-axis. Translation in the z-direction may be achieved using either traditional leadscrew actuators or faster piezoelectric actuators (e.g., Physik Instrumente P-725 or Thorlabs PFM450E). However, it is unclear if this approach may be used to achieve higher z-scanning speeds, as it requires accelerating the relatively large moving mass of the microscope objective. In addition, when used with fragile biological samples and liquid immersion objectives, the z-scanning speed must frequently be further limited to avoid sample movement and damage. Multiple approaches have been explored for accelerating volumetric imaging, including varifocal lenses [6-14], remote focusing [15,16], extended depth of field microscopy [17,18], tomography [19], and holographic microscopy [20]. Varifocal lenses are relatively simple and compatible with common imaging modalities, making them an especially promising approach for performing fast z-scanning. Most commonly, a varifocal lens is positioned either directly behind the microscope objective or at a pupil located within the microscope body, and changes in the lens power produce rapid movement of the focal plane while maintaining the microscope

Automated summary

This study develops an analytical approximation for predicting tuning-induced spherical and axial chromatic aberration in optical systems containing a tunable lens element. The model shows that correcting both aberrations can be achieved by controlling specific parameters. These insights are used to design an axial-scanning microscope system with high numerical aperture and diffraction-limited performance.