We introduce a transmissive refractive adaptive optics system featuring a deformable transparent optofluidic wavefront modulator and a sensorless wavefront error estimation algorithm. The wavefront modulator consists of a cavity filled with an optical liquid which is sealed by a deformable elastic polymer membrane. Deformation of the membrane is achieved through electrostatic actuation using 25 transparent indium tin oxide electrodes buried in the cavity. Modulation of the two-dimensional phase distribution generated by the system is performed using open loop control both with and without active wavefront sensing. For the latter, a progressive modal decomposition algorithm is used to estimate and correct distortion in the point-spread function (PSF) of the wavefront arising due to the optical system and other sources of wavefront distortion. Using this control method, we experimentally demonstrate high-fidelity recreation of Zernike modes up to the fourth order, and blind (sensorless) PSF correction in a wide-field microscope.
The shape of liquid interfaces can be precisely controlled using electrowetting, an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises. We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit, a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts. This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets. The 1.5 mm long slit aperture, with controllably variable discrete widths down to 45 µm, may be scanned across a length of 1.5 mm with switching times between adjacent slit positions of less than 120 ms. In addition, for a fixed slit aperture position, the width may be tuned to a minimum of 3 µm with high uniformity and linearity over the entire slit length. This compact, purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size.
Adaptive optics (AO) is a powerful image correction technique with proven benefits for many life-science microscopy methods. However, the complexity of adding a reflective wavefront modulator and a wavefront sensor into already complicated microscope has made AO prohibitive for its widespread adaptation in microscopy systems. We present here the design and performance of a compact fluorescence microscope using a fully refractive optofluidic wavefront modulator yielding imaging performance on par with that of conventional deformable mirrors, both in correction fidelity and articulation. We combine this device with a modal sensorless wavefront estimation algorithm that uses spatial frequency content of acquired images as a quality metric and thereby demonstrate a completely in-line adaptive optics microscope which can perform aberration correction up to 4 th radial order of Zernike modes. This entirely new concept for adaptive optics microscopy may prove to extend the performance limits and widespread applicability of AO in life science imaging.
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