Diffraction-limited deep focusing into biological tissue is challenging due to aberrations that lead to a broadening of the focal spot. The diffraction limit can be restored by employing aberration correction for example with a deformable mirror. However, this results in a bulky setup due to the required beam folding. We propose a bi-actuator adaptive lens that simultaneously enables axial scanning and the correction of specimen-induced spherical aberrations with a compact setup. Using the bi-actuator lens in a confocal microscope, we show diffraction-limited axial scanning up to 340 μm deep inside a phantom specimen. The application of this technique to in vivo measurements of zebrafish embryos with reporter-gene-driven fluorescence in a thyroid gland reveals substructures of the thyroid follicles, indicating that the bi-actuator adaptive lens is a meaningful supplement to the existing adaptive optics toolset.

Electrically tunable lenses exhibit strong potential for fast motion-free axial scanning in a variety of microscopes. However, they also lead to a degradation of the achievable resolution because of aberrations and misalignment between illumination and detection optics that are induced by the scan itself. Additionally, the typically nonlinear relation between actuation voltage and axial displacement leads to over- or under-sampled frame acquisition in most microscopic techniques because of their static depth-of-field. To overcome these limitations, we present an Adaptive-Lens-High-and-Low-frequency (AL-HiLo) microscope that enables volumetric measurements employing an electrically tunable lens. By using speckle-patterned illumination, we ensure stability against aberrations of the electrically tunable lens. Its depth-of-field can be adjusted a-posteriori and hence enables to create flexible scans, which compensates for irregular axial measurement positions. The adaptive HiLo microscope provides an axial scanning range of 1 mm with an axial resolution of about 4 μm and sub-micron lateral resolution over the full scanning range. Proof of concept measurements at home-built specimens as well as zebrafish embryos with reporter gene-driven fluorescence in the thyroid gland are shown.

In this paper we present and verify the non-linear simulation of an aspherical adaptive lens based on a piezo-glass sandwich membrane with combined bending and buckling actuation. To predict the full non-linear piezoelectric behavior, we measured the non-linear charge coefficient, hysteresis and creep effects of the piezo material and inserted them into the FEM model using a virtual electric field. We further included and discussed the fabrication parameters -glue layers and thermal stress -and their variations. To verify our simulations, we fabricated and measured a set of lenses with different geometries, where we found good agreement and show that their qualitative behavior is also well described by a simple analytical model. We finally discuss the effects of the geometry on the electric response and find, e.g., an increased focal power range from ±4.5 to ±9 m −1 when changing the aperture from 14 to 10 mm.

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We present two piezo-actuated adaptive prisms with apertures of 8 mm based on a bi-axial continuously tiltable glass window on top of an optical fluid, enabling fast scanning applications in a compact, linear axial design. One prism with a device size of 58 by 51 mm is optimized for scan angles of ±6.4 • and response times of 2.5 ms. A second compact prism uses spiral-shaped actuators to achieve a reduced device diameter of 33 mm at slightly compromised maximum scan angles of ±4.0 • with response times of approximately 4 ms. We show the design and FEM-based optimization of the prisms, their fabrication and the characterization of the scan angles and of the dynamic behavior. Finally, we also demonstrate the linearity of the system and discuss a simple control model.