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

Chromatic aberration correction based on cross-channel information alignment in microscopy

A microscope usually consists of dozens of complex lenses and requires careful assembly, alignment, and testing before use. Chromatic aberration correction is a significant step in the design of microscopes. Reducing chromatic aberration by improving optical design will inevitably increase the overall weight and size of the microscope, leading to more cost in manufacturing and maintenance. Nevertheless, the improvement in hardware can only achieve limited correction. In this paper, we propose an algorithm based on cross-channel information alignment to shift some of the correction tasks from optical design to post-processing. Additionally, a quantitative framework is established to evaluate the performance of the chromatic aberration algorithm. Our algorithm outperforms the other state-of-the-art methods in both visual appearance and objective assessments. The results indicate that the proposed algorithm can effectively obtain higher-quality images without changing the hardware or engaging the optical parameters.

Volumetric light sheet imaging with adaptive optics correction

Light sheet microscopy has developed quickly over the past decades and become a popular method for imaging live model organisms and other thick biological tissues. For rapid volumetric imaging, an electrically tunable lens can be used to rapidly change the imaging plane in the sample. For larger fields of view and higher NA objectives, the electrically tunable lens introduces aberrations in the system, particularly away from the nominal focus and off-axis. Here, we describe a system that employs an electrically tunable lens and adaptive optics to image over a volume of 499 × 499 × 192 μm3 with close to diffraction-limited resolution. Compared to the system without adaptive optics, the performance shows an increase in signal to background ratio by a factor of 3.5. While the system currently requires 7s/volume, it should be straightforward to increase the imaging speed to under 1s per volume.

Tunable doublets: piezoelectric glass membrane lenses with an achromatic and spherical aberration control

We present two versions of tunable achromatic doublets based on each two piezoelectrically actuated glass membranes that create the surface of fluid volumes with different dispersions: a straightforward back-to-back and a more intricate stack of the fluid volumes. In both cases, we can control the chromatic focal shift and focal power independently by a suitable combination of actuation voltages on both active membranes. The doublets have a large aperture of 12 mm at an outer diameter of the actuator of 18 mm, an overall thickness of 3 mm and a short response time of around 0.5 ms and, in addition, provide spherical aberration correction. The two designs have an achromatic focal power range of ±2.2 m^-1 and ±3.2 m^-1 or, for the purpose of actively correcting chromatic errors, a chromatic focal shift at vanishing combined focal power of up to ±0.08 m^-1 and ±0.12 m^-1.

VIS-NIR superachromatic triplet design with five-color correction for a broadband interferometer

In general, k lenses with different materials can achieve at most (k+1) color correction (k≥2). A superachromat containing three lenses is designed to achieve five-color correction in the 600-1600 nm waveband, where the maximum chromatic focal shift is controlled within 1/100,000 of the focal length, achieving an almost unprecedented result. Conditions for lens power combination of three thin lenses in contact are first derived based on the Buchdahl dispersion equation; then a metric is introduced to verify the five-color correction, and a correction method is proposed to improve the refractive index fitting accuracy of the Buchdahl model from ∼10^-3 to ∼10^-7. By traversing 197 ecofriendly glass materials in the CDGM glass library iteratively, 113 initial structures are obtained in only 61.75 s, from which the structure with the minimum chromatic focal shift is selected to be optimized with Opticstudio. By setting up required operands, the final structure being within the diffraction limit in a field of view of ±0.05^∘ is obtained within only 6 s, where the maximum longitudinal chromatic aberration is close to the maximum chromatic focal shift. We provide a complete theoretical basis and important guidance for designing broadband superachromats with (k+2) color correction using only k lenses and the smallest chromatic focal shift, and based on the theories, we have developed a broadband interferometer.

Generalised adaptive optics method for high-NA aberration-free refocusing in refractive-index-mismatched media

Phase aberrations are introduced when focusing by a high-numerical aperture (NA) objective lens into refractive-index-mismatched (RIM) media. The axial focus position in these media can be adjusted through either optical remote-focusing or mechanical stage translation. Despite the wide interest in remote-focusing, no generalised control algorithm using Zernike polynomials has been presented that performs independent remote-focusing and RIM correction in combination with mechanical stage translation. In this work, we thoroughly review derivations that model high-NA defocus and RIM aberration. We show through both numerical simulation and experimental results that optical remote-focusing using an adaptive device and mechanical stage translation are not optically equivalent processes, such that one cannot fully compensate for the other without additional aberration compensation. We further establish new orthogonal modes formulated using conventional Zernike modes and discuss its device programming to control high-NA remote-focusing and RIM correction as independent primary modes in combination with mechanical stage translation for aberration-free refocusing. Numerical simulations are performed, and control algorithms are validated experimentally by fabricating graphitic features in diamond using direct laser writing.