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.

Adaptive lenses offer fast and flexible scans without mechanical movement. However, driving the lens to achieve the desired behavior is challenging and requires online monitoring. The demand for monitoring techniques can be high when lenses with large tuning ranges or multiple degrees of freedom are employed. We analyze the performance of a partitioned aperture wavefront (PAW) as a tool for in situ and in-process monitoring of adaptive lenses. PAW has the advantage of enabling measurements of large input wavefront angles and thus high-tuning-range lenses with just a single beam path. PAW is used to characterize an adaptive lens with a high tuning range of ± 20 d p t and for controlling the behavior of a novel adaptive lens with two actuators that allow for the tuning of focal length and spherical aberrations simultaneously.

Due to their high stiffness-to-weight ratio, glass fiber-reinforced polymers are an attractive material for rotors, e.g., in the aerospace industry. A fundamental understanding of the material behavior requires non-contact, in-situ dynamic deformation measurements. The high surface speeds and particularly the translucence of the material limit the usability of conventional optical measurement techniques. We demonstrate that the laser Doppler distance sensor provides a powerful and reliable tool for monitoring radial expansion at fast rotating translucent materials. We find that backscattering in material volume does not lead to secondary signals as surface scattering results in degradation of the measurement volume inside the translucent medium. This ensures that the acquired signal contains information of the rotor surface only, as long as the sample surface is rough enough. Dynamic deformation measurements of fast-rotating fiber-reinforced polymer composite rotors with surface speeds of more than 300 m/s underline the potential of the laser Doppler sensor.

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